- PHYLUM ECHINODERMATA - . GENERAL CHARACTERISTICS

- PHYLUM ECHINODERMATA - . GENERAL CHARACTERISTICS

-
.
Around t h e i r base a r e many modified
w i t h an epidermis.
spines, the p e d i c e l l a r i a , which resemble t i n y jaws o r
scissor blades mounted on a s t a l k .
When stimulated
mechanically o r chemically, the p e d i c e l l a r i a may be
opened by muscles. Their f u n c t i o n i s t o keep t h e aboral
surface clean, t o a i d i n t h e capture o f small food
p a r t i c l e s and p r o t e c t the dermal papulae which a r e t h i n walled extensions o f the coelom and f a c i l i t a t e gaseous
exchange.
PHYLUM ECHINODERMATA
-.
-
"
GENERAL CHARACTERISTICS
Spiny-skinned animals possessing calcareous o s s i c l e s
embedded i n t h e dermis and spines p r o t r u d i n g from the
surface: t h i s creates an i n t e r n a l skeleton.
They are r a d i a l l y symnetrical i n the a d u l t phase and a r e
characterized by having f i v e rays, o r m u l t i p l e s o f f i v e
(pentamerous).
This penta-symnetry i s most apparent i n
s t a r f i s h and Least apparent i n sea cucunbers.
WATER VASCULAR SYSTEM
The water vascular system i s a d i v i s i o n o f t h e coelom and
i s unique t o echinoderms. I t i s e s s e n t i a l l y a system o f
hollow interconnected tubes f i l l e d w i t h water. The water
i s under a s l i g h t p o s i t i v e pressure.
Water enters the
system v i a the madreporite on t h e aboral disc. The water
vascular system terminates i n a t u b e - f e e t (Podia) i n the
grooves on the o r a l surface. The sequence o f canals i n
t h e water vascular system i s as follows:
Echinoderms have n o t always been r a d i a l l y symnetrical:
f o s s i l forms a r e b i l a t e r a l l y symnetrical ( w i t h a l e f t and
r i g h t sides and a f r o n t and back).
Echinoderm Larval
stages ( b i p i n n a r i a ) a r e a l s o b i l a t e r a l l y symnetrical.
Body w a l l s a r e cornposed o f t h r e e layers o f c e l l s . Most
tissues a r e c i l i a t e d . There i s no head region, b r a i n nor
segmentation.
1 Madreporite (sieves the water)
I Stone Canal (runs downwards)
1 Ring Canal ( e n c i r c l e s the mouth)
1 5 Radial Canals (one per r a y arm)
1 Numerous Transverse Canals (perpendicular t o r a d i a l
cana 1)
1 Ampullae: The head o f the tube f e e t .
A l l examples a r e marine and t h e r e a r e no p a r a s i t i c forms.
ALL have tube f e e t which extend by h y d r a u l i c pressure
from t h e animal's water vascular system, which are used
v a r i o u s l y f o r Locomotion, burrowing, exchange o f gases
( r e s p i r a t i o n ) and feeding.
The water vascular system i s a h y d r a u l i c pressure system.
The s t a r f i s h moves by means o f i t s tube feet.
A tube
f e e t elongates as the muscles surrounding the ampullae
contract f o r c i n g f l u i d i n t o the foot.
On t h e bottom o f
the f o o t i s a sucker which adheres t o t h e substratum
( s t i c k secretions from the gland c e l l s a t t h e t i p a i d i n
adhesion).
Longitudinal
muscles
then contract,
shortening the r a y arm and h e l p p u l l t h e s t a r f i s h
forward. The combined e f f e c t s o f forward t h r u s t s o f many
co-ordinated tube-feet
produce
Locomotion i n the
starfish.
The d i g e s t i v e t r a c t i s simple u s u a l l y complete (but may
Lack an anus and t h e r e f o r e be incomplete).
Respiration i s achieved by minute g i l l s (dermal papulae)
which protrude from t h e coelom, by tube f e e t and i n the
case o f sea cucumbers by a cloaca1 r e s p i r a t o r y trees.
A c i r c u l a t o r y system r a d i a t e s from t h e c e n t r a l coelom,
the coelom i s Lined w i t h c i l i a t e d peritoneum and i s
u s u a l l y Large and i t s f l u i d contains f r e e amoebocytes.
Part o f t h e Larval coelom becomes a water vascular system
u s u a l l y having many tube feet, serving f o r Locomotion,
food handling, o r r e s p i r a t i o n .
Tube f e e t are a l s o used f o r c a p t u r i n g and handling food,
and f o r r e s p i r a t i o n and excretion. There a r e a l s o n i n e
small spherical swellings c a l l e d t h e tiedemannls bodies
on the inner r i n g canal.
2
The nervous system c o n s i s t s o f a circum o r a l r i n g and
r a d i a l nerves i n t o each arm.
The sexes a r e separate ( r a r e exceptions), and a l i k e
externally; gonads a r e Large w i t h simple ducts; ova are
abundant.
The l a r v a i s free-swimning,
and i s
characterized by a conspicuous metamorphosis t o become
adults.
A few species are viviparous, a few reproduce
asexually by s e l f - d i v i s i o n , and many regenerate Lost
parts readily.
For example s t a r f i s h are generally
capable o f r e p l a c i n g one o r more Lost arms; sometimes,
even a s i n g l e arm can regenerate i n t o an e n t i r e animal.
GENERAL STRUCTURE OF A STARFISH (ASTEROIDEA)
EXTERNAL
The Lower surface w i t h t h e mouth i s c a l l e d the o r a l
surface. The upper surface w i t h the anus i s c a l l e d the
aboral surface.
Both t h e mouth and anus are c e n t r a l l y
situated.
ORAL SURFACE
Has f i v e ambulacral grooves, one i n each r a y from which
extends two o r four rows o f tube-feet.
The r a y may be
f l e x e d s l o w l y by a few r e t r a c t o r muscles i n the body
wall.
ABORAL SURFACE
Many spines o f various sizes, p e d i c e l l a r i a e and dermal
papulae a t t h e base o f t h e spines, a madreporite which i s
the entrance t o the water vascular system and an anal
opening.
DIGESTIVE SYSTEM
+
This i s a short b u t complete system
I Mouth
1 Short oesophagus
1 Thin w a l l stomach
l a r g e Cardiac stomach
small aboral P y l o r i c
I From the P y l o r i c a tube passes i n t o each r a y
1 I n each r a y arm i t d i v i d e s i n t o two branches
hepatic cecae from here
I many Lateral pouches e x i s t .
I Above the stomach i s a slender i n t e s t i n e
1 s p l i t s i n t o two branched pouches, the r e c t a l
i n t e s t i n a l cecae
1 Anus
-r
-r
stomach
arm.
called
and
FOOD
S t a r f i s h eat almost any animal matter, and are a l s o
carnivorous on oysters, mussels, barnacles, clams etc.
SMALL FOOD passes d i r e c t l y
p e d i c e l l a r i a o r tube feet.
to
the
mouth
via
the
BIVALVES the s t a r f i s h opens the s h e l l halves s l i g h t l y
using i t s rayiarms and tube f e e t . The cardiac stomach i s
everted between t h e gap i n t h e s h e l l halves. D i g e s t i v e
enzymes are released and t h e prey t i s s u e i s broken down
i n t o a f l u i d which i s swept i n t o t h e h e p a t i c cecae by the
action o f c i l i a .
N u t r i e n t s a r e s t o r e d i n t h e hepatic
ceca.
INTERNAL SYSTEM
INTERNAL TRANSPORT
An endoskeleton o f calcareous p l a t e s o r o s s i c l e s i s bound
together by muscles and connective tissue.
Uses the f l u i d mediun o f t h e p e r i v i s c e r a l coelom.
The aboral calcareous spines are short, b l u n t and covered
Amoebocytes (coelomocytes) a s s i s t
i n the transport o f
5
n u t r i e n t s and wastes.
rows o f tube-feet they are d i s t r i b u t e d b i l a t e r a l l y .
C
RESPIRATION
SEA LILIES CLASS CRINOIDEA: occur as f r e e l i v i n g forms
(feather s t a r ) o r s e s s i l e forms (sea L i l i e s ) .
These
animals are h i g h l y c a l c i f i e d , and generally occur i n deep
waters. They c o l l e c t food by c i l i a r y currents set up on
t h e i r complex arms. Tube f e e t are present only as small
p a p i l l a e on t h e sides o f the ambulacral grooves.
--
Gaseous exchange between dermal papulae and tube feet.
Dermal papulae are outpockets o f t h e coelom t h a t pass
through minute openings i n t h e skeleton.
They are
covered w i t h c i l i a on the i n t e r n a l and external surfaces.
The external c i l i a keep a current o f oxygenated water
passing over the outside,
and t h e i n t e r n a l c i l i a
c i r c u l a t e t h e coelomic f l u i d i n t o t h e papulae.
SEA DAISIES CLASS CONCENTRICYCLOIDEA: c o n s i s t o f a d i s c
The water
shaped body without arms, mouth o r anus.
vascular system possesses two r i n g canals concentric on
the v e n t r a l surface.
EXCRETION
=
-
e
Amnonia i s t h e p r i n c i p a l s o l u b l e nitrogenous waste, and
i t d i f f u s e s through t h i n areas o f t h e body surface,
e s p e c i a l l y tube f e e t and dermal papulae.
Particulate
waste are picked up by the amoebocytes w i t h i n the coelom;
these amoebocytes are subsequently eliminated through the
walls o f t h e dermal papulae.
NERVOUS SYSTEM AND SENSE ORGANS
This consists o f interconnected peripheral and c e n t r a l
components. The p e r i p h e r a l nervous system i s composed o f
a subepidermal nerve net t h a t extends throughout the
body, i n c l u d i n g t h e tube feet. This system c o n t r o l s l o c a l
responses o f t h e pedicel lariae,
spines and dermal
branchiae t o s p e c i f i c s t i m u l i .
L a t e r a l t r a c t s conduct
neural impulses a t higher speeds t o and from the c e n t r a l
nervous system. This consists o f a nerve r i n g around the
mouth plus f i v e l a r g e r a d i a l nerves t h a t run p a r a l l e l t o
t h e r a d i a l canals o f t h e water vascular system.
c
2
-
Most echinoderms respond t o touch, gravity, l i g h t and
chemical s t i m u l i .
Yet t h e sense organs are poorly
developed.
The primary receptors are sensory c e l l s
Located i n t h e epidermis, e s p e c i a l l y on t h e podia and t h e
margins o f t h e ambulacral grooves.
At t h e end o f each
ray i s a small t a c t i l e t e n t a c l e and a l i g h t s e n s i t i v e
eyespot composed o f 80 t o 200 o c e l l i . Most echinoderms
are negatively phototaxic and generally seek shade.
REPRODUCTION AND REGENERATION
Sexes are separate. A p a i r o f branched gonads L i e i n the
p e r i v i s c e r a l coelom a t t h e base o f each arm.
Female
s t a r f i s h may release up t o 2,5 m i l l i o n eggs a t one time.
Males produce even more sperm.
F e r t i l i z a t i o n and
development occurs external l y i n t h e seawater.
Echinoderm development:
f e r t i l i z e d c e l l * cleavage =
two-egg stage -r b l a s t u l a * gastrula * b i p i n n a r i a *
branchiolaria
*
undergoes
metamorphosis
*
pentasymnetrical s t a r f i s h .
OTHER ECHINODERMS
BRITTLE STARS CLASS OPHIUROIDEA: possess f i v e arms
r a d i a t i n g from a c e n t r a l disc, the arms are more sharply
formed.
Tube f e e t Lack suckers, movement effected
c h i e f l y by movement o f t h e arms brought about by muscles
which connect successive ambulacral ossicles. They are
d e t r i t u s feeders, having a capacious stomach but Lack any
extension o f t h e gut i n t o t h e arms and Lack an anus.
SEA URCHINS CLASS ECHINOIDEA: have a r i g i d body wall o r
t e s t composed o f c l o s e l y f i t t i n g calcareous p l a t e s
embedded i n the dermis.
The o r a l surface i s
morphologically very Large compared t o t h e aboral
surface. The mouth i s surrounded by powerful jaws which
can scrape o f f encrusting organisms from t h e rocks. The
spines borne on t h e t e s t are Long and movable and are
interspersed w i t h p e d i c e l l a r i a . The numerous tube f e e t
are very e x t e n s i b l e and p r o j e c t beyond the spines.
SEA CUCUMBERS CLASS HOLOTHUROIDEA: possess reduced dermal
ossicles.
They feed on d e t r i t u s , which they take i n t o
the mouth by Large modified tube f e e t surrounding i t .
The remaining tube f e e t resemble those o f the s t a r f i s h
and are used f o r Locomotion.
Although there are f i v e
NOTE: CLASSES ASTEROIDEA and OPHIUROIDEA are sometimes
considered t o be subclasses i n the CLASS STELLEROIDEA
PHYLUM CHAETOGNATHA ARROW WORMS
Arrow worms, are named f o r t h e i r streamlined appearance.
They are about 40 mn i n Length and completely transparent
b i l a t e r a l l y symnetrical deuterostomes. Their r e l a t i o n s h i p
t o echinoderms, hemichordates o r chordates i s unclear.
Arrow worms are important planktonic predators, feeding
voraciously on copepods, f i s h f r y and each other;
they
capture t h e i r prey using b r i s t l e s ( c h a i t e ) around t h e i r
They possess a hood which they can draw
jaws (gnathos).
over t h e i r b r i s t l e s and jaws t o streamline t h e i r bodies.
Swimning i s due t o the a l t e r n a t i n g contractions o f the
l o n g i t u d i n a l muscles on each side.
The f i n s are f i r m l y
attached t o t h e i r Lateral sides o f t h e body.
The
digestive t r a c t i s straight.
The nervous system
comprises a v e n t r a l ganglia i n t h e trunk and a dorsal
ganglia i n the head region and several smaller ganglia.
Sensory b r i s t l e s d i s t r i b u t e d over t h e body detect prey,
and a c i l i a r y Loop t h a t passes beneath t h e head Like a
necklace i s thought t o detect water currents o r
chemicals.
Two dorsal eyes ( o c e l l i ) presumably detect
Light and c o n t r o l the v e r t i c a l m i g r a t i o n a t dawn and
dusk. Arrow worms are hermaphroditic, w i t h two ovaries
i n the trunk coelom and two testes i n t h e t a i l coelom.
Sperm are packaged i n t o spermatophytes and are released
by simply breaking through t h e body wall.
These
spermatophores then attach t o the a n t e r i o r trunk o f the
same o r a d i f f e r e n t individual, and t h e sperm migrate
i n t o t h e ovaries.
F e r t i l i z a t i o n i s therefore internal.
There are no excretory, c i r c u l a t o r y o r r e s p i r a t o r y
organs.
PHYLUM HEMICHORDATA
This group o f animals share several s i m i l a r i t i e s w i t h the
chordates which includes pharyngeal s l i t s and a dorsal
nerve cord and were once c l a s s i f i e d as chordates since i t
was thought t h a t they a l s o possessed a notochord. Recent
analysis has i d e n t i f i e d what was once considered a
notochord t o be an extension o f the buccal c a v i t y ( t h e
buccal d i v e r t i c u l u n ) .
Nevertheless t h e hemichordates
appear t o have diverged close t o a p o i n t a t which the
chordates originated.
Hemichordates are d i v i d e d i n t o two classes t h a t d i f f e r
g r e a t l y from each other, although they show s i m i l a r
s t r u c t u r e i n e a r l y embryological stages.
Class Enteropneusta includes most o f the phylun, and are
comnonly r e f e r r e d t o as acornworms. These animals burrow
i n marine sediments and have worm-like bodies d i v i d e d
i n t o a proboscis, c o l l a r , and trunk.
The other Class
Pterobranchia Live i n colonies and secrete tubes.
ACORN WORMS GENERAL FEATURES
Possess a prominent proboscis, a c o l l a r and a long slimy
trunk up t o 2 metres i n Length.
Each o f these three
regions have a separate coelomic compartment f i l l e d with
spongy t i s s u e that provides some mechanical support,
nevertheless these animals are e a s i l y broken.
Acorn
worms e i t h e r Live i n U-shaped burrows i n shallow water o r
they burrow through marine sediment o r Live under rocks
o r seaweed.
.
A
,'.The proboscis i s the main organ o f Locomotion, with the
trunk being p u l l e d along passively.
Many acorn worms
feed by i n g e s t i n g Large q u a n t i t i e s o f mud o r sand from
which the gut e x t r a c t s organic debris. Others feed by
means o f c i l i a on t h e proboscis which pass the food
backwards i n t o the mouth. Food p a r t i c l e s are bound on a
mrcous s t r i n g and are swallowed along w i t h the water.
The chordates are b i l a t e r a l l y symnetrical, w i t h three
germ Layers, a segmented body, complete d i g e s t i v e
t r a c t , and w e l l developed coelom. The f o l l o w i n g three
c h a r a c t e r i s t i c s apply:-
*
A s i n g l e dorsal t u b u l a r nerve cord.
A notochord.
ACORN WORM INTERNAL STRUCTURE
G i l l s l i t s i n the pharynx
Uater swal lowed d u r i n g feeding e x i t s through pharyngeal
s l i t s and g i l l pores. The pharyngeal s l i t s are U-shaped
openings i n the pharynx t h a t can swallow water i n t o the
pharyngeal pouches and out through the g i l l pores.
Pharyngeal s l i t s are sometimes c a l l e d g i l l s l i t s ,
although i n these animals they have a feeding r o l e rather
than f o r t h e exchange o f r e s p i r a t o r y gases.
The body
: surface i s t h e main route f o r r e s p i r a t o r y exchange. The
colourless blood i s punped a n t e r i o r l y by a dorsal vessel
i n t o a c o n t r a c t i n g heart vessel i n the proboscis and then
p o s t e r i o r l y by a v e n t r a l vessel.
The blood c i r c u l a t e s
; through sinuses, making i t an open c i r c u l a t o r y system.
One such sinus, the glomerulus, i s assuned t o have an
excretory function. The nervous system consists Largely
of a d i f f u s e network i n the base o f the epidermis. Along
the dorsal and v e n t r a l midlines t h i s plexus i s
concentrated i n t o dorsal and v e n t r a l nerve cords which
Lack ganglia.
I n places the nerve cord i s hollow and
s i m i l a r t o the hollow d o r s a l nerve o f the chordates.
Sensory receptors are s c a t t e r e d over the integunent,
e s p e c i a l l y around the proboscis.
Sexes are separate i n ,
the acorn worms, although t h e r e i s L i t t l e t o d i s t i n g u i s h
males from females.
The gonads have a separate
gonadopore, and f e r t i l i z a t i o n i s external and achieved
through mass spawning i n i t i a t e d by the females.
Embryological development i s t y p i c a l deuterostome. This
i s characterized by r a d i a l cleavage, the blastopore
becoming the anus, and the coelom forms and outpocketing
o f the archenteron.
Development i s sometimes d i r e c t ,
although more u s u a l l y a t o r n a r i a Larva develops
characterized by c i l i a r y contractions which cause i t t o
spin.
The t o r n a r i a Larva c l o s e l y resembles the
b i p i n n a r i a n Larva o f the echinoderms.
PTEROBRANCHIA
There are about t e n species i n t h i s class and they have
a s i m i l a r development t o the acorn worms w i t h t h e i r
bodies d i v i d e d i n t o a proboscis, c o l l a r and trunk.
However, the adult, external appearance i s very d i f f e r e n t
from acorn worms.
The c o l l a r expands d o r s a l l y i n t o
tentacled arms which possess c i l i a t h a t d i r e c t food i n t o
c i l i a t e d grooves which c a r r y i t t o the mouth.
The
alimentary canal i s U-shaped w i t h the anus outside the
f r i n g e of tentacles.
I n most species there i s only one
p a i r o f pharyngeal s l i t s .
Some pterobranchia are dioecious,
but most are
hermaphroditic. Although f e r t i l i z a t i o n i s external, the
embryos g e n e r a l l y remain s h e l t e r e d w i t h i n the tubes. The
sexually produced i n d i v i d u a l s then g i v e r i s e t o colonies
by budding.
These t i n y marine animals tend t o form l a r g e p l a n t Like
colonies, whose i n d i v i d u a l s p r o j e c t Like small flowers a t
the ends o f a branching s e r i e s o f tubes. The short body
i s doubled-back on i t s e l f , so t h a t the anus opens
a n t e r i o r l y over t h e back o f the head.
I t i s generally
believed t h a t they are a very p r i m i t i v e group rather than
a degenerate hemichordate. Modern hemichordates appear
t o be very s i m i l a r t o the f o s s i l g r a p t o l i t e s which were
abundant i n the seas around the f i r s t f o s s i l evidence o f
the vertebrates.
THE LOWER CHORDATES (UROCHORDATES & CEPHALOCHORDATES)
Small-sized marine animals e i t h e r being s e s s i l e
( t u n i c a t e s ) o r f r e e - l i v i n g (Lancelets).
ORIGINS
D i p l o b l a s t i c animals (u
coelenterates) may be the
most ancestral c o n d i t i o n since i t Lacks a middle Layer,
the mesoderm. Higher animals a1 1 have a mesoderm and
t r i p l o b l a s t i c . From the mesoderm muscular, s k e l e t a l and
c i r c u l a t o r y systems are formed. There a r e two types of
embryonic formation which allows f o r t h e development of
t h i s Layer. I n echinoderms, chaetognaths,
hemichordates and chordates the mesoderm a r i s e s from
pouches growing outwards from the w a l l s o f the gut.
These pouches remain i n the a d u l t as closed body
c a v i t i e s . I n a l l other animals t h e mesoderm formation
a r i s e s as s o l i d masses o f c e l l s budded o f f from an area
near the p o s t e r i o r end o f the body, and the body c a v i t y
a r i s e s by cleavage w i t h i n the mass o f the mesodermal
c e l l s . This mesodermal development occurs i n molluscs
and annelids, with the arthropods having a h i g h l y
modified p a t t e r n o f development. A c l a d i s t i c
c l a s s i f i c a t i o n would separate the echinoderms and
chordates ( i n c l u d i n g hemichordates) as being the major
d e v i a t i o n with the r e s t of the i n v e r t e b r a t e s developing
independently.
From t h i s theory the d i v i s i o n o f
echinoderms and hemichordates from the other
invertebrates i s r e f l e c t e d by t h e i r p a t t e r n o f
cleavage, method of g a s t r u l a t i o n , and Larval
development. This theory suggests t h a t chordates
evolved d i r e c t l y from the most p r i m i t i v e metazoans, but
t h i s would imply t h a t the middle body Layer, a t r u e
body cavity, mouth and anus a l l evolved separately i n
the echinoderms and protochordates and the other
invertebrates.
Resemblances between the lower chordates and same
invertebrates have been the basis f o r several other
theories o f chordate o r i g i n s .
Annelid theory. Annelids and chordates are both
b i L a t e r a l l y symnetrical and segmented, w i t h segmental
excretory organs, a well-developed coelom, and
Longitudinal blood vessels.
I n v e r t i n g an annelid would
place i t s nerve chord dorsal t o the d i g e s t i v e t r a c t ,
and the path o f blood flow would resemble t h a t o f
chordates; however, the mouth would then be dorsal,
u n l i k e a chordate, and other dorsoventral r e l a t i o n s
would be altered. Annelids, moreover, have no
s t r u c t u r e s suggestive of the notochord o r g i 11 s l i t s .
Arthropod theory. Based on the steady progression o f
forms from the simple invertebrates t o hunans as the
most advanced L i f e forms. According t o the theory the
arthropod-chordate theory, an arthropod became i n v e r t e d
so t h a t the dorsal heart and v e n t r a l nerve cord became
the chordate's v e n t r a l heart and dorsal nerve. The
same problems o f t h i s theory e x i s t as t h a t f o r the
annelid theory.
Arachnid theory. Arachnids are thought t o have
descended from an annelid ancestry. However, t h i s
theory has the same problem o f the v e n t r a l nerve cord
r e q u i r i n g the reversal o f dorsal and v e n t r a l surfaces.
The segmentation i s s t i l l wrong, t h e r e i s no traces o f
the notochord and i n t e r n a l g i l l s . The arthropod's
j o i n t e d Legs could not have evolved i n t o the f i s h ' s
fins.
Echinoderm theory. s i m i l a r i t i e s o f the echinoderms t o
the chordates include the indeterminate and r a d i a l
cleavage. The t o r n a r i a Larva o f hemichordates and the
b i l a t e r a l b i p i n n a r i a Larva o f echinoderms a r e both
minute and transparent, w i t h almost i d e n t i c a l external
1
4
=
c i l i a t e d bands and a Like nunber o f coelomic c a v i t i e s ;
both a l s o having a dorsal pore. Even p r o t e i n s o f the
blood serun are more c l o s e l y matched between
hemichordates and echinoderms. Even the phosphorous
compounds t h a t speed up the release of energy f o r
muscle a c t i v i t y are s i m i l a r .
A hypothetical sequence could be:
Hemichordate Larva
Echinoderm ( a u r i c u l a r i a ) Larva
tunicate Larva * amphioxus + ostracoderm
+
+
The problem i s t h a t the anatomy o f the L i v i n g
echinoderms i s v e r y d i f f e r e n t t o hemichordates and
protochordates. Ancestral echinoderms were, however,
n e i t h e r r a d i a l l y symnetrical nor arranged i n groups o f
f i v e nor where they a l l f r e e - l i v i n g . I n f a c t the
p r i m i t i v e echinoderm Cothurnocystis appears t o be
c l o s e l y r e l a t e d t o the pterobranchia.
Garstangls theory f o r the o r i g i n o f the vertebrates
=
Branchiostoma (anphioxus) i s a small f i s h - l i k e marine
animal (70 mn i n Length) occurring i n t r o p i c a l and
temperate waters, and normally found p a r t l y b u r i e d i n
sand. These animals are a l l f r e e swimning, possess a
pronounced notochord, have major blood vessels t h a t are
s i m i l a r t o t h a t of a f i s h , have m u l t i p l e g i l l s l i t s and
a pharynx t h a t i s h i g h l y s p e c i a l i z e d f o r f i l t e r i n g . The
g i l l s are therefore more o f a feeding r a t h e r than a
r e s p i r a t i o n device.
The o r i g i n o f t h e vertebrates i s about as u n c e r t a i n as
the o r i g i n o f the chordates. For many years amphioxus
was viewed as a L i v i n g r e l a t i v e f o r the vertebrate
ancestors. I n a d d i t i o n t o having a l l the
c h a r a c t e r i s t i c s o f t h e chordates, the a d u l t amphioxus
also has resemblance t o the vertebrates.
It i s
generally agreed now t h a t the vertebrates are more
l i k e l y t o have evolved from the other protochordate
group, the Urochordates which include the t u n i c a t e seas q u i r t s ( r e d b a i t ) . Although the a d u l t i s a s e s s i l e
animal t h a t i n no way appears t o resemble any other
vertebrate, i t s f r e e swimning Larvae does. Garstang
suggested t h a t t h i s urochordate acquired the a b i l i t y t o
reproduce w h i l s t s t i l l a f r e e - l i v i n g Larvae and became
the ancestor t o the vertebrates. The process o f a
Larval stage being able t o reproduce i s c a l l e d
paedomorphosis and i s not u n c m n i n chordates.
Although Garstangls theory i s the most widely
supported, there i s no r e a l evidence and a l t e r n a t i v e
theories f o r v e r t e b r a t e e v o l u t i o n include d i r e c t
descendance from the e x t i n c t echinoderm group
Calcichordates.
Another a l t e r n a t i v e i s based on the embryonic
developnent o f vertebrates which has remained somewhat
of a mystery; namely t h a t the embryonic o r i g i n s o f
p a r t s o f the head, e s p e c i a l l y sense organs, muscles,
and s t r u c t u r e s involved i n gas exchange, d i f f e r from
those i n the r e s t o f the body. I t i s therefore
suggested t h a t v e r t e b r a t e evolved from an amphioxus
l i k e protochordate i n which the head gradually
elaborated d u r i n g a t r a n s i t i o n from f i l t e r feeding t o
a c t i v e predation.
SUBPHYLUM UROCHORDATA: CLASS ASCIDIACEA
s t o l o n i f e r a , Red-bait, p r e f e r s wave-beaten
shores, presumably because the water movement aids the
c i r c u l a t i o n o f water through i t s pharynx and ensures an
adequate supply o f suspended food p a r t i c l e s . Not only
does r e d - b a i t t h r i v e i n t u r b u l e n t waters, but the s i z e
i t reaches i s d i r e c t l y r e l a t e d t o the amount of surge
i t receives; i n c e r t a i n areas where wave a c t i o n i s
p a r t i c u l a r l y strong, i t can reach 20 cm i n size.
i s a s o l i t a r y tunicate, although they Live i n
crowded groups each animal i s an independent u n i t .
Each i n d i v i d u a l animal i s enclosed i n a t h i c k
p r o t e c t i v e t e s t which i s attached t o the substrate by a
holdfast. The t e s t has two dorsal t e a t - l i k e s t r u c t u r e s
a t the apex which are the openings t o the buccal and
a t r i a l siphons. Water i s drawn i n through the buccal
c a v i t y and f i l t e r e d by the pharynx, and passes out
through the a t r i a l siphon. The l a r v a i s f r e e swimning
and s i m i l a r t o amphioxus.
U n l i k e f i s h , emphioxus has no Lateral p a i r e d f i n s , b u t
does have a dorsal f i n t h a t extends the e n t i r e Length
of the body, a caudal f i n and a v e n t r a l f i n . A L L f i n s
are strengthened by a dense connective t i s s u e t h a t
forms f i n rays.
The body w a l l s are d i v i d e d i n t o IoVooshaped muscle
segments c a l l e d myotomes, which are separated from each
other by connective tissue. They are arranged
a l t e r n a t i v e l y on e i t h e r s i d e o f the body. Contraction
of the myotomes produces Lateral body movements
necessary f o r swimning.
The protruding mouth i s surrounded by an o r a l hood from
which p r o j e c t c i l i a t e d o r a l t e n t a c l e s ( c i r r i ) .
The anus opens on the L e f t s i d e o f the body near t o the
base o f the caudal f i n .
The s k e l e t a l system i s composed o f a w e l l developed
notochord, a rod of dense connective t i s s u e l y i n g
dorsal t o the d i g e s t i v e t r a c t .
Amphioxusls food consists o f minute organisms t h a t are
f i l t e r fed i n t o the mouth by water c u r r e n t s produced by
the c i l i a on the g i l l s . The d i g e s t i v e system consists
o f a mouth which Leads t o a pharynx which has w a l l s
pierced by 180 p a i r s o f g i l l s l i t s which sieve food
from the water. A v e n t r a l c i l i a t e d groove, the
endostyle secretes mucous. C i l i a conveys mucous up and
over the g i l l bars and entraps food p a r t i c l e s . The
c i l i a then pass the food-laden mucous i n t o the stomach.
B l i n d hepatic cecae emerge from the stomach. There i s
a s t r a i g h t i n t e s t i n e which Leads t o t h e anus.
The c i r c u l a t o r y system i s s i m i l a r t o t h a t o f a f i s h ,
except t h a t i t Lacks the two charrrbered heart, but
contains open sinuses.
A s u b i n t e s t i n a l v e i n c o l l e c t s n u t r i e n t Laden blood from
the i n t e s t i n e and c a r r i e s i t forward t o the hepaticp o r t a l v e i n and then t o the hepatic caecwn. The
hepatic caecum Leads t o the v e n t r a l a o r t a which i s
purped by rhythmical contractions i n t o t h e a f f e r e n t
branchial a r t e r i e s t h a t supply the g i l l bars. I t then
passes onto the e f f e r e n t branchial a r t e r i e s and onto
the paired dorsal aortae. The blood i s oxygenated
during the passage through the g i l l s and i s then taken
back i n t o the dorsal aorta. The dorsal aorta d i v i d e s
by way o f i n t e s t i n a l capi 1l a r i e s i n t o the s u b i n t e s t i n a l
vein.
The d i r e c t i o n o f the blood i s t h e r e f o r e p o s t e r i o r i n
the dorsal vessels and a n t e r i o r i n t h e v e n t r a l vessels.
Respiration occurs i n the pharynx which i s attached
d o r s a l l y and hangs i n t o a c a v i t y c a l l e d the a t r i u m
which i s Lined w i t h ectodermal epithelium. Water i s
drawn through the mouth i n t o the pharynx and goes
through the g i l l s l i t s i n t o the a t r i u n e x i t i n g through
the atriopore. The g i l l s l i t s are framed by c i l i a t e d
g i l l bars supported by rods o f dense connective tissue.
The exchange of r e s p i r a t o r y gases occurs through the
g i l l slits.
Other UROCHORDATE CLASSES a r e LARVACEA and THALlACEA
The excretory system i s composed o f s i n p l e nephridia
that are s i t u a t e d d o r s a l l y - l a t e r a l l y . Each bears
c l u s t e r s o f f l a g e l l a t e d flame c e l l s . There are about
100 nephridia connected t o the d o r s a l coelom w i t h i n the
a t r i a l cavity.
CEPHALOCHORDATA EXAMPLE BRANCHIOSTOMA (AMPHIOXUS)
The nervous system consists o f a c e n t r a l nerve cord
t h a t runs dorsal t o t h e d i g e s t i v e t r a c t and r e s t i n g on
the notochord.
The c e n t r a l canal transverses t h e e n t i r e Length and
widens a t t h e a n t e r i o r end t o form a cerebral v e s i c l e
( l o c a t i o n o f t h e brain).
Two p a i r s o f sensory nerves
a r i s e from the v e s i c l e and serve t h e a n t e r i o r end. The
r e s t o f t h e nerve cord gives o f f t h e nerves on the
opposite sides t h a t a l t e r n a t e with each other. These
nerves are o f two kinds, the dorsal nerves with a
sensory f u n c t i o n and t h e v e n t r a l nerves w i t h a motor
function.
Sense organs include:
1) O l f a c t o r y p i t
2) Epidermal sensory & l l s on the o r a l and
v e l a r tentacles
3) Rows o f simple eyes ( 1 ganglion and 1
pigment c e l l )
The reproductive system i s composed o f p a i r e d gonads
t h a t p r o j e c t i n t o t h e atrium. The sexes are separate
and the egg and sperm c e l l s are discharged i n t o the
a t r i a l c a v i t y and reach t h e e x t e r i o r v i a an atriopore.
F e r t i l i z a t i o n i s external.
The r e s t o f t h e chordates, c o l l e c t i v e l y r e f e r r e d t o as
the vertebrata a l l have an enlarged b r a i n enclosed i n a
b r a i n case, o r craniun, and a segmented spinal c o l m
o f vertebrae t h a t become t h e a x i a l support o f t h e body.
T y p i c a l l y t h e body comprises a head, neck, trunk, and a
t a i l . These classes show a progressive series o f
s t r u c t u r a l and f u n c t i o n a l advances i n a l l organ systems
besides the features o f the notochord and g i l l s l i t s .
1) The body covering i s a s t r a t i f i e d epithelium and
dermis, w i t h many mucous glands i n aquatic species;
most f i s h e s are covered w i t h p r o t e c t i v e scales; the
e x t e r i o r i s c o r n i f i e d on Land dwellers, with scales on
r e p t i l e s , feathers on b i r d s and h a i r on mamnals;
feathers and h a i r form i n s u l a t e d body coverings.
2) The i n t e r n a l and j o i n t e d skeleton i s o f c a r t i l a g e
i n Lower vertebrates and o f bone i n higher groups; i t
supports and p r o t e c t s various organs; the cranium
s h e l t e r s t h e b r a i n and has p a i r e d capsules t o contain
organs o f special sense; a s e r i e s o f v i s c e r a l arches
supports t h e g i l l region, and c e r t a i n arches become the
jaws and other s t r u c t u r e s o f t h e head region; t h e
v e r t e b r a l column extends from the base o f the cranium
t o the end o f t h e t a i l and has neural arches d o r s a l l y
t o house t h e nerve cord. Two p a i r s o f appendages, the
f i n s o f f i s h e s and Limbs o f tetrapods, w i t h j o i n t e d
s k e l e t a l supports, are a r t i c u l a t e d with the v e r t e b r a l
c o l m through Limb g i r d l e s .
3) On t h e skeleton are muscles t h a t move i t s p a r t s and
provide f o r Locomotion.
4) The Long d i g e s t i v e t r a c t i s v e n t r a l t o the
v e r t e b r a l c o l m ; the mouth contains a tongue and
u s u a l l y teeth; the anus opens a t the end o f the trunk;
the Liver and pancreas are two Large d i g e s t i v e glands
that pour t h e i r secretions through ducts joined t o t h e
intestine.
5 ) The c i r c u l a t o r y system includes a well-developed
muscular heart o f two, three, o r four chambers, Located
v e n t r a l l y t o t h e d i g e s t i v e t r a c t ; i t s contractions
propel the blood through a closed system of arteries,
c a p i l l a r i e s , and veins, the flow being a n t e r i o r l y on
the v e n t r a l s i d e and p o s t e r i o r l y i n the dorsal
arteries; t h e blood plasma contains both white and red
corpuscles, t h e L a t t e r w i t h haemoglobin as a
r e s p i r a t o r y pigment; a system o f Lymph vessels i s
present; p a i r e d a o r t i c arches transport blood from t h e
heart t o t h e g i l l s i n Lower vertebrates; progressive
separation o f t h e r e s p i r a t i o n (pulmonary) and systemic
blood paths through t h e heart Leads t o r e a l i z a t i o n of
regulated body temperature i n t h e warm blooded
(homeothermat) b i r d s and mamnals.
6) Respiration i n the Lower forms i s by p a i r e d g i l l s ;
t e r r e s t r i a l species have Lungs developed from
outpocketings o f the d i g e s t i v e t r a c t .
7)
The paired excretory organs, o r kidneys, discharge
through duct openings near o r through t h e anus; i n
lower forms, the organs are o f segmental nature and
d r a i n wastes from both the coelom and t h e blood; i n
higher forms they are non-segmental and d r a i n o n l y from
the blood; a bladder f o r storage o f u r i n e occurs i n
many.
8) The b r a i n becomes r e g i o n a l l y d i f f e r e n t i a t e d as t o
s t r u c t u r e and function; the cerebral hemispheres and
cerebellum enlarge, e s p e c i a l l y i n higher forms; there
are 10 o r 12 p a i r s o f c r a n i a l nerves i n t h e head t h a t
serve both motor and sensory function, i n c l u d i n g t h e
paired organs of special senses (smell, sight, and
hearing plus e q u i l i b r a t i o n ) ; from the nerve cord a p a i r
of spinal nerves serves each p r i m i t i v e body somite; an
autonomic nervous system regulates i n v o l u n t a r y
functions o f i n t e r n a l organs.
9) A series o f endocrine glands (thyroid, p i t u i t a r y ,
e t c ) provides hormones, transported by t h e blood
stream, t h a t regulate b o d i l y processes, growth, and
reproduction.
10) With r a r e exceptions t h e sexes are separate, and
each has a p a i r o f gonads t h a t discharge sex c e l l s
through ducts opening i n t o o r near t h e anus.
SUBPHYLUM VERTEBRATA: CLASS AGNATHA
Two Living representative, the Lamprey (order
Petromyzontida and Hagfish (phylogenetic r e l a t i o n s h i p s
are unclear but has been put i n t o the order Myxinida).
Lampreys are both marine and fresh water, whereas
hagfish are e x c l u s i v e l y marine. These Lowest o f Living
vertebrates Lack t r u e jaws, and t h e i r nearest a l l i e s
are the ancient ostracoderms o f t h e S i l u r i a n and
Devonian times. The Lamprey-hagfish Lines o f e v o l u t i o n
diverged e a r l y and probably had separate o r i g i n s among
the ostracoderm ancestors.
Lampreys and hagfish are p r i m i t i v e animals because they
Lack paired f i n s , they posses p o o r l y developed
c a r t i l a g i n o u s skeletons, they have a s i n g l e n o s t r i l and
they Lack jaws.
Both Lampreys and hagfish are h i g h l y modified
( p a r t i c u l a r l y i n the v i c i n i t y o f t h e mouthparts) f o r
p a r a s i t i z i n g (Lamprey) and scavenging (hagfish).
The
ancestral form however, was probably f i l t e r - f e e d i n g
Ostracoderms.
OSTRACODERMS
These animals were f i r s t found i n t h e mid-Ordovician
(500 t o 450 m i l l i o n years ago). Their c h a r a c t e r i s t i c s
include:
A s i n g l e dorsal n o s t r i l
They were without p a i r e d appendages ( f i n s ) , but some
had peculiar f l a p s p r o j e c t i n g from behind t h e head.
ALL had a bony armour o r scales and i n some t h e head
contained an i n t e r n a l skeleton of bone. This suggests
t h a t bone i s an archaic feature d a t i n g t o t h e e v o l u t i o n
o f the f i r s t vertebrates. The bony armour may have
provided p r o t e c t i o n against ancient water scorpions
(e.g.Pterygotus). Other suggestions are t h a t t h e
armour prevented undue water Loss o r represented a
store of calciun salts.
L i k e a l l agnathans, they Lacked jaws, however, t h e i r
pharynx possessed paired g i l l s l i t s .
They possessed a dorsal s p i n a l cord, and notochord.
; ' The head region o f some possessed a pronounced dorsal
Land Lateral sensory f i e l d s Leading t o speculation t h a t
@'
they could generate e l e c t r i c f i e l d s .
-
=
They evolved i n t o a great nunber o f forms varying from
f l a t bottom-dwelling animals t o a c t i v e f a s t swimning
animals (Birkenia). Some forms even Lost t h e i r bony
p l a t e s and became covered w i t h minute d e n t i c l e s
(Thelodus).
opening
.
NERVOUS SYSTEM
The b r a i n i s p r i m i t i v e , dominated by f o r e b r a i n w i t h a
Large p a i r o f o l f a c t o r y Lobes. The cerebral
hemispheres are attached t o a diencephalon, and there
i s a v e n t r a l l y attached broad infund.ibulun and above i t
a pineal structure. The midbrain possesses a l a r g e
p a i r o f o p t i c Lobes, and t h e h i n d b r a i n has rudimentary
cerebellun. There are ten p a i r s o f c r a n i a l nerves.
LAMPREY (ORDER PETROMYZONTIDA)
SENSE ORGANS
EXTERNAL FEATURES
*
Body i s c y l i n d r i c a l w i t h a L a t e r a l l y compressed t a i l
possessing a caudal f i n . The s k i n i s without scales,
but has an epidermal gland which produces the slimy
secretions. There i s a row o f sensory p i t s forming a
Lateral Line. The mouth i s h i g h l y modified and
consists o f s u c t o r i a l disc, a mouth t h a t i s h e l d open
by a r i n g o f c a r t i l a g e , bordered by sensory p a p i l l a e
and horny l1teethl1 Like structures. From t h e mouth
protrudes a p i s t o n - l i k e tongue. There are a p a i r o f
eyes, s i n g l e nasal opening and seven g i l l s l i t s . The
anus i s on t h e v e n t r a l surface j u s t behind the
urogenital opening.
SKELETAL SYSTEM
A notochord p e r s i s t s throughout. The a x i a l skeleton i s
composed o f small c a r t i l a g i n o u s neural arches, with the
head supported and protected by a c a r t i l a g e s k u l l .
A
c a r t i l a g e branchial basket p r o t e c t s t h e g i l l s . There
i s stout c a r t i l a g e i n the tongue.
MUSCULAR SYSTEM
Short segmented muscles which appear t o have a IgZgg
shape i n s i d e view. A l t e r n a t e contractions produce
rhythmic Lateral movement o f t h e f l a n k s which propel
the animal forward. Radial muscles surround the mouth
and r e t r a c t o r muscles occur i n t h e tongue.
DIGESTIVE SYSTEM
Oral d i s c and i t s horny t e e t h attach the Lamprey t o
other f i s h . The tongue rasps i n t o the f l e s h o f the
f i s h using i t s r e t r a c t o r muscles. The d i g e s t i v e system
consists o f an oesophagus, a v e n t r a l pharynx, no
d i f f e r e n t i a t e d stomach, a Long s t r a i t i n t e s t i n e which
has i n t e r n a l s p i r a l l y arranged f o l d s (typhlosole) which
increases surface area f o r absorption. The d i g e s t i v e
system terminates i n an anus. A Liver i s present i n
association w i t h t h e d i g e s t i v e system.
CIRCULATORY SYSTEM
Consists o f heart, a r t e r i e s , veins and Lymphatic
sinuses. The heart Lies i n the p e r i c a r d i a l c a v i t y and
consists o f an a t r i u n which receives blood and
v e n t r i c l e which pumps blood.
RESPIRATORY SYSTEM
Seven p a i r s o f g i l l pouches which open i n t e r n a l l y i n t o
the pharynx and e x t e r n a l l y v i a the g i l l s l i t s . There
are numerous g i l l filaments supplied w i t h c a p i l l a r i e s .
Gaseous exchange occurs as water passes through the
g i l l pouches. Water i s drawn i n t o the g i l l pouch
through t h e g i l l s l i t s (an adaptation t o a p a r a s i t i c
L i f e r e q u i r i n g t h a t the mouth be attached t o a host).
The Larval Lamprey ( c a l l e d an amnocoete) i s not
p a r a s i t i c , and water passes through t h e mouth and over
the g i l l s ( t h e p a t t e r n t h a t occurs i n bony f i s h ) .
EXCRETORY SYSTEM
Linked with t h e reproductive system (= urogenital
system).
The kidneys L i e along t h e dorsal wall o f the
body. U r i n e passes v i a a u r i n a r y duct i n t o the g e n i t a l
sinus which opens t o the e x t e r i o r v i a a urogenital
The o l f a c t o r y sac i s contained i n the nasal capsule and
i s connected t o the outside through t h e s i n g l e nasal
opening occurring on the dorsal surface. There i s a
balancing organ which l i e s i n the a u d i t o r y capsule and
consists o f two semicircular canals. The eyes are
p r i m i t i v e , yet allow good vision. P o s t e r i o r t o the
nasal opening i s t h e pineal eye w i t h a Lens and a
pigmented r e t i n a . The pigments o f t h e eye vary with
the Lamprey switching from Rhodopsin under marine
conditions t o Porphyropsin under freshwater conditions.
Lampreys are also able t o produce e l e c t r i c a l f i e l d s .
REPRODUCTION
The sexes are separate, with t h e gonad being
protandric, t h a t i s f i r s t producing male gametes and
then female gametes w i t h i n t h e same i n d i v i d u a l . A
s i n g l e Large Long gonad f i l l s t h e abdominal cavity.
There are no g e n i t a l ducts, w i t h egg o r sperm being
discharged i n t o abdominal c a v i t y and passes through
paired g e n i t a l pores i n t o t h e u r o g e n i t a l sinus and t h e
passes outside the body external f e r t i l i z a t i o n takes
place. Spawning always occurs i n freshwater, w i t h a
female lamprey producing up t o 100 000 eggs. A f t e r
spawning the female Lampreys die. The eggs hatch i n t o
a Larvae c a l l e d t h e amnocoete and remain i n t h i s
condition f o r 3 t o 12 years. The Larva obtains i t s
food through i n s p i r a t i o n o f water and using mucous t o
entangle t h e food and pass i t t o t h e small i n t e s t i n e
( i n a very s i m i l a r fashion t o t h a t o f amphioxus).
The
amnocoete Larva undergoes metamorphosis t o become an
a d u l t Lamprey and t h e returns t o t h e sea.
The lamprey d i f f e r s from t h e hagfish which has a mouth
t h a t i s surrounded by sensory tentacles and a l s o has a
varying nunber o f g i l l pouches ( f i v e t o f i f t e e n ) .
CLASS PLACOOERMI
These are Large, h e a v i l y armoured f i s h possessing jaws,
and were possibly the f i r s t vertebrates t o possess them
( t h i s may, however, be i n dispute).
The r i s e o f the
placoderms probably c o n t r i b u t e d t o t h e e x t i n c t i o n o f
the ostracoderms. These f i s h a l s o characterized the
f i r s t attempts a t developing p a i r e d limbs. There were
many experiments with appendages, although many
placoderms were s t i l l without f i n s , but s t i l l possessed
Large hollow f i x e d spines p r o j e c t i n g outwards from the
shoulder regions. Most placoderms were predatory f i s h
and some reached 10 metres i n length. The most
c h a r a c t e r i s t i c feature are the heavy armour p l a t e s on
the outside, e s p e c i a l l y around t h e head. I n some o f
these bony p l a t e s served t h e f u n c t i o n o f jaws and
teeth, o r even Large crushing plates. The placoderms
were f a r removed from the main evolutionary Line o f the
vertebrates. Therefore, few, i f any, o f t h e known
types can be considered ancestral t o Later vertebrates.
An ancestral form may have Lost i t s p l a t e s o f bony
armour, and could have given r i s e t o the sharks and
chimaeras.
-
The appendicular skeleton includes a V
shaped
pectoral g i r d l e supporting t h e pectoral f i n s , a
f l a t t e r p e l v i c g i r d l e w i t h f i n s and a smaller
j o i n t e d c a r t i l a g e which provides i n t e r n a l
support f o r the Lateral f i n s .
CLASS CHONDRICHTHYES (Cartilaginous f i s h )
CURRENTLY THE MOST PRIMITIVE VERTEBRATES UHICH POSSESS
t
Complete and separate vertebrates
t
Movable jaws
MUSCULAR SYSTEM
t
Paired appendages
Body and t a i l muscles segmented
ADVANCES OVER THE CLASS AGNATHA
t
Scales (placoid) covering the body
t
Two p a i r s o f Lateral f i n s
t
t
Movable jaws which a r t i c u l a t e w i t h the craniun
Enamel covered teeth
t
Three semicircular canals
DIGESTIVE SYSTEM
MWTH
Teeth derived from modified p l a c o i d scales,
replacement teeth develop continuously
F l a t tongue adhere t o the f l o o r o f the mouth.
On the sides o f t h e wide pharynx are openings
Leading t o separate g i l l s l i t s and spiracles.
Short oesophagus leading t o a "Jl1 shaped
stomach which ends w i t h a c i r c u l a r sphincter
muscle ( p y l o r i c valve)
I n t e s t i n e f o l l o w s and i s connected t o a cloaca
and anus.
I n t e s t i n e contains a s p i r a l valve, which i s
covered by a mucous membrane which slows down
the food and increases absorptive surfaces.
L i v e r has two Long Lobes, secretes b i l e v i a a
duct and a conspicuous g a l l bladder exists.
Pancreas Lies between t h e stomach and the
intestine, i t s duct j o i n i n g the l a t t e r j u s t
below the b i l e duct.
A r e c t a l gland attaches d o r s a l l y a t the
junction o f the i n t e s t i n e and the cloaca and
removes excess s a l t from t h e blood.
Paired reproductive organs
LESS ADVANCED THAN A BONY FISH (CLASS OSTEICHTHYES)
SINCE
t
Skeleton i s made o n l y o f c a r t i l a g e
t
P l a c o i d scales o n l y
t
Separate g i l l c l e f t s
t
Possesses a p a i r o f s p i r a c l e s connected t o the
pharynx
t
Has no swim bladder
COELOM (Body Cavity)
EXAMPLE IS THE DOGFISH (SQUALUS)
t
Stomach, intestine, and other i n t e r n a l organs
l i e i n the Large body c a v i t y o r coelom.
t
I t i s l i n e d w i t h a smooth membrane: t h e
peritoneun and t h i s covers the organs.
t
The peritoneum i s supported from the mid dorsal
wall o f the coelom by t h i n mesenteries.
t
The transverse septun separates coelom from the
c a v i t y containing t h e heart.
EXTERNAL FEATURES
t
t
t
t
t
t
t
Blunt pointed head
Trunk s p i n d l e shaped
Two separate median dorsal f i n s
A median caudal f i n
Two p a i r s o f l a t e r a l f i n s (pectoral and p e l v i c )
Mature males have a clasper on t h e i r p e l v i c
fins
Anal f i n
CIRCULATORY SYSTEM
HEAD
t
t
t
t
t
Two n o s t r i l s
L a t e r a l eyes without e y e l i d s
Five oval g i l l s l i t s open a n t e r i o r l y t o each
pectoral f i n
S p i r a c l e ( g i l l c l e f t ) opens behind each eye
The heart i s beneath t h e g i l l region: consists
o f a t h i n - w a l l e d dorsal sinus venosa t h a t
receives blood, followed by t h e a t r i u n , then
the t h i c k walled v e n t r i c l e and t h e conus
arteriosus.
Blood passes a n t e r i o r l y i n t o t h e v e n t r a l aorta
where f i v e p a i r s o f a f f e r e n t branchial a r t e r i e s
d i s t r i b u t e t o the c a p i l l a r i e s i n t h e g i l l s f o r
aeration, four p a i r s o f e f f e r e n t branchial
a r t e r i e s c o l l e c t blood i n t o the dorsal aorta
which extends along mid-dorsal w a l l o f the
coelom.
BODY COVERING
Diagonal rows o f minute p l a c o i d scales, each backward
p o i n t i n g and covered wi.th enamel over a base p l a t e o f
dentine.
SKELETON
P r i n c i p a l a r t e r i e s are:
t
C a r t i l a g e r e i n f o r c e d w i t h limy deposits
t
A x i a l skeletons: s k u l l / v e r t e b r a l c o l m , w i t h
each vertebra having a spool shaped centrun,
concaved a t both ends, a neural arch housing
t h e nerve cord. The notochord p e r s i s t s i n
spaces between t h e vertebrae.
t
t
t
b
t
t
The s k u l l i s composed o f a cranium housing the
brain, possesses p a i r e d capsules f o r olfactory,
o p t i c and a u d i t o r y organs. The v i s c e r a l
skeleton consists o f jaws, the hyoid arch and
f i v e p a i r s o f branchial arches supporting the
g i l l region.
t
Paired e x t e r n a l / i n t e r n a l c a r o t i d s -. head
Paired subclavians -. p e c t o r a l f i n s
Coelic -. stomach, l i v e r , i n t e s t i n e
Anterior mesenteric -. spleen and p o s t e r i o r
intestine
Posterior mesenteric -, t o r e c t a l gland
Renal and gonadic -. t o kidneys/reproductive
organs
Paired i l i a c s -. p e l v i c f i n s
MIDBRAIN
P r i n c i p a l veins
F
b
b
b
b
Paired renal p o r t a l
kidneys
Paired postcardinal + p a r a l l e l i n g the kidneys
Paired Lateral abdominal veins
e i t h e r side o f
t h e body c a v i t y
Jugular and a n t e r i o r cardinal veins (sinuses)
r e t u r n blood from the head region
Blood from t h e d i g e s t i v e t r a c t flows v i a the
hepatic p o r t a l v e i n and i s f i l t e r e d through the
l i v e r and then i s c o l l e c t e d i n the hepatic
veins which are connected t o the sinus venosus.
+
+
RESPIRATORY SYSTEM
F
By opening and c l o s i n g t h e mouth, sharks draw
i n water and passes i t out through t h e g i l l
s l i t s and spiracles.
b
Two rounded Lobes d o r s a l l y s i t u a t e d
HINDBRAIN
b
b
F
b
b
Large median dorsal cerebellun over t h e opentopped medulla oblongata
Eleven c r a n i a l nerves (one t o t e n p l u s zero)
Spinal nerve protected by vertebrae
Paired spinal nerves t o each body segment
Sympathetic nervous system: s e r i e s o f ganglia,
roughly segmental above t h e postcardinal veins.
REPRODUCTIVE SYSTEM
SEXES ARE SEPARATE
The g i l l s are composed o f many p a r a l l e l ,
slender filaments t h a t contain c a p i l l a r i e s .
Male sperm develops i n long t e s t e s
From each testes vasa deferens runs p o s t e r i o r l y
on the v e n t r a l surface o f t h e kidney and
empties i n t o the u r o g e n i t a l p a p i l l a .
Blood from the v e n t r a l aorta passes through
these c a p i l l a r i e s , discharges carbon dioxide
and absorbs oxygen dissolved i n water, then
continues i n t h e dorsal aorta.
At mating claspers are placed close together,
and they are inserted i n t o t h e cloaca o f the
females. Seminal f l u i d flows down the canal
formed by t h e adjacent clasper grooves.
EXCRETORY SYSTEM
b
The two slender kidneys L i e imnediately above
the coelom on e i t h e r s i d e o f t h e dorsal aorta.
b
U r i n e from each kidney i s c o l l e c t e d i n a series
o f segmental tubules t h a t j o i n a l o n g i t u d i n a l
duct, t h e ureter, Leading p o s t e r i o r l y ; t h e two
u r e t e r s empty through a s i n g l e urogenital
p a p i l l a , Located d o r s a l l y i n the cloaca.
b
Females have two l a r g e ovaries, two oviducts
extend the length of t h e body cavity, t h e i r
a n t e r i o r ends j o i n i n a s i n g l e l a r g e funnel
through which the eggs enter. The forward p a r t
o f the each duct i s d i l a t e d as a s h e l l gland,
and i n ovoviviparous species, Like the dog f i s h
the p o s t e r i o r p a r t i s enlarged as a 88uterus88
to
contain the young during development. The
oviducts open separately i n t o the cloaca.
CLASSIFICATION OF CHONDRICHTHYES
.
SENSE ORGANS
b
Two n o s t r i l s ( o l f a c t o r y sacs)
b
Pharynx: scattered t a s t e buds
b
Eyes:
b
b
I1Ear"
Lateral
Line
moved by three p a i r s o f muscles
attaching t h e eyeball t o i t s socket and
are without l i d s . Retina composed o f
rods only, therefore no colour v i s i o n
i s possible.
Organ o f ba 1ance
Three s e m i - c i r c u l a r canals
A f i n e groove along each s i d e o f t h e
trunk and Line t a i l . Contains a slender
canal w i t h many small openings t o the
surface. W i t h i n t h e canal are sensory
h a i r s connecting t o a branch o f t h e
tenth c r a n i a l nerve. They respond t o
Low frequency pressure s t i m u l i i n t h e
surrounding water. On the head are
other sensory canals opening by senses
pores; each pore Leads t o a small
chamber (Ampulla o f Lorenzini)
containing an electroreceptor w i t h
sensory h a i r s connecting t o nerve
fibres.
SUBCLASS ELASMOBRANCHII
ORDER CLADOSELACHIDA
ORDER XENACANTHIDA
E a r l y f r e s h water
sharks
* Extinct *
ORDER GALEOMORPHA
L i v i n g sharks
Mollusc feeding forms
Nurse sharks
Modern sharks
(great whites)
Tiger sharks
S i x - g i l l e d sharks
ORDER SQUALOMORPHA
Dogfish and small
r e l a t e d sharks
ORDER BATOIDEA
Skates and rays;
Ibbottom L i v i n g formsbb
flattened
dorsoventral ly,
pectoral f i n s enlarged
and Locomotion i s
achieved through
undulations, Lost the
caudal fins; no
Lateral thrashing o f
the t a i l . Mouth on
bottom. Water brought
i n v i a s p i r a c l e s on
dorsal surface (behind
the eyes)
NERVWS SYSTEM
More advanced than the lamprey.
FOREBRAIN
b
F
b
b
b
Two o l f a c t o r y sacs
Large o l f a c t o r y t r a c t s + o l f a c t o r y Lobe
Paired cerebral hemispheres on t h e diencephalon
Dorsal p i n e a l body
Ventral infundibulun and hypophysis
Ancestral sharks,
appeared i n t h e
Devonian. Paired f i n s
but no claspers.
* Extinct *
SUBCLASS HOLOCEPALI
S h a r k - l i k e but w i t h crushing
tooth plates. Most forms are
extinct.
ORDER CHIMAERIDA
Chimaeras o r r a t f i s h ,
Flap o f s k i n covering
the separate branchial
slits.
w
SPINY SHARKS CLASS ACANTHODIANS
Heart i s two chambered (one a t r i u n and one
v e n t r i c l e ) . I n association w i t h t h e heart i s a
sinus venosa and conus arteriosus. Heart
contains only venous blood; red blood c e l l s are
nucleated and oval.
These may w e l l have been t h e e a r l i e s t gnathostomes
(vertebrates w i t h t r u e jaws).
They were small f i s h
which s u p e r f i c i a l l y resembled sharks. While the
contemporary placoderms a l s o had jaws, the acanthodian
jaw i s b a s i c a l l y t h e same as t h a t o f the bony f i s h
(Class Osteichthyes).
I t i s also thought t h a t they had
Lungs with which they used f o r e i t h e r breathing or as
h y d r o s t a t i c organs ( f u n c t i o n a l swim bladders?).
-
The e a r l y acanthodians are t y p i f i e d by the genus
Climatius which was f i r s t found i n the Late S i l u r i a n
period. They were small, o n l y a few centimetres i n
Length. Their bodies are t y p i c a l l y f i s h - l i k e (spindleshaped) w i t h t h e p o s t e r i o r body being t i l t e d upwards,
with the caudal f i n being underneath c r e a t i n g a t y p i c a l
heterocercal t a i l . There were two Large t r i a n g u l a r
dorsal median f i n s , f i v e p a i r e d v e n t r a l median f i n s as
well as p a i r e d pectoral and p e l v i c f i n s . Climatius was
protected by a dermal armour o f small rhombic o r
diamond-shaped scales which covered the e n t i r e body and
continued over t h e head i n t h e form o f r e g u l a r l y
arranged plates. These f i s h were characterized by
extremely Large eyes r e l a t i v e t o t h e i r body s i z e and
eyes t h a t are placed f a r forward. I n contrast the
nasal region f o r o l f a c t o r y senses were rather poorly
developed. The upper jaw was generally o s s i f i e d and
well developed. On the sides o f the heads were the
g i l l coverings o r opercular flaps, one t o each o f the
f i v e g i 11 arches, a d over these there were larger
opercular coverings o f s t i f f bony rods.
Although Climatius represents a p r i m i t i v e ancestral
form the acanthodians d i v e r s i f i e d i n the same ways t h a t
the bony f i s h have; namely Long slender e e l - l i k e forms
t o deep-bodied f a s t swimning forms.
I n some there was
a Loss o f t h e p a i r e d f i n s and a tremendous exaggeration
o f the dorsal f i n spines.
Skeleton c h i e f l y o f bone ( c a r t i l a g e i n
Vertebrae a r e many and
p r i m i t i v e sturgeons).
d i s t i n c t ; t a i l u s u a l l y homocercal (even-sized
above and below caudal vertebrae).
Primitive
f i s h o f t e n have heterocercal t a i l s (caudal
vertebrae bend upwards) R e l i c t s o f a notochord
many s t i l l p e r s i s t .
Respiration i s by p a i r s o f g i l l s on bony g i l l
arches contained w i t h i n a comnon chamber on
each side o f the pharynx and covered by a bony
operculun. Usually possess a swim bladder
which sometimes has a duct connecting t o t h e
pharynx. I n some f i s h t h e swim bladder i s a
Lungfish),
t r u e Lung (Dipnoi f i s h :
i n d i c a t i n g t h a t t h e e a r l i e s t f i s h had Lungs.
b
b
Cranial nerves zero t o t e n are present.
Body temperature dependent on envirorment and
behaviour ( p o i k i lothermal) may be elevated i n
Large a c t i v e f i s h .
Gonads t y p i c a l l y paired; u s u a l l y oviparous
(some ovovivaparous and viviparous forms),
f e r t i l i z a t i o n u s u a l l y external (exceptions
exist).
Eggs are u s u a l l y minute but can be
Large such as t h e 100 mn eggs o f t h e
Coelacanth.
PHYLOGENY OF OSTEICHTHYES
Divided i n t o
SUBCLASS SARCOPTERYGII
Divided i n t o
Acanthodian were most abundant i n the Devonian and
thereafter d e c l i n e d and were e x t i n c t by the end o f the
Palaeozoic.
The phylogenetic r e l a t i o n s h i p o f these f i s h t o the
other jawed f i s h e s (placoderms, c a r t i l a g i n o u s and bony
f i s h ) i s unclear.
I t i s now generally excepted that
they belong t o a class o f t h e i r own, but they have
s i g n i f i c a n t r e l a t i o n s h i p s w i t h osteichthyes (*
opercular flaps, jaws and p a i r e d f i n s ) .
BONY FISH CLASS OSTEICHTHYES
CHARACTERISTICS
b
Skin w i t h many mucous glands, u s u a l l y w i t h
embedded bony dermal scales (Ganoid i n
p r i m i t i v e forms, otherwise c y c l o i d o r ctenoid);
some f i s h have Lost t h e i r scales; both median
and p a i r e d f i n s are present (some exceptions
and modifications), f i n s are supported by f i n
rays composed o f c a r t i l a g e o r bone; no Limbs.
Mouth u s u a l l y terminal and possessing teeth;
jaws w e l l developed and a r t i c u l a t e d t o the
s k u l l ; two o l f a c t o r y sacs t h a t are s i t u a t e d
d o r s a l l y and are u s u a l l y not connected t o the
mouth cavity; eyes are u s u a l l y w e l l developed
possessing rods and cones ( t h e L a t t e r f o r
colour v i s i o n ) and not possessing eyelids.
F i n - r a y f i s h = SUBCLASS ACTINOPTERYGII
Lobe-finned = SUBCLASS SARCOPTERYGII
ORDER CROSSOPTERYGII
SUBORDER COELACANTHINI
SUBORDER RHIPIDISTIA
(These were t h e
ancestors t o t h e
tetrapods)
ORDER DIPNOI (Lungfish)
CROSSOPTERYGII
These were the most comnon f i s h i n t h e Devonian times.
Generally these f i s h were aggressive, predacious f i s h ,
t h a t were ancestral t o the tetrapods (amphibian and
above groups).
They had already become r a r e by the
Carboniferous times and w i t h one exception were e x t i n c t
by the close o f the Palaeozoic.
The coelacanths are stub-nosed. small iawed f i s h which
although once though t o be e x t i n c t are-now known t o be
the only Living Crossopterygian species.
I n 1939 a
Coelacanth species was found o f the coast o f South
A f r i c a (East London). This species has been c l a s s i f i e d
i n the genus Latimeria and represents the closest f i s h
r e l a t i v e t o the tetrapods (four-Legged animals).
Latimeria i s a h i g h l y specialized deep sea f i s h , whose
d i s t a n t ancestors would have evolved towards t h e
tetrapod structure. Coelacanths are very u n l i k e the
Crossopterygians o f t h e Devonian times t h a t evolved
towards the amphibian condition. These Devonian
Crossopterygians possessed a s k u l l which had a passage
that Linked the n o s t r i l w i t h the roof o f i t s mouth.
ALL tetrapods have t h i s feature and confirm t h a t these
f i s h were on the evolutionary Line t h a t Lead t o the
f i r s t Land vertebrates ( t h e amphi bians represented by
an animal c a l l e d Eusthenopteron).
.
good o l f a c t o r y senses and a L a t e r a l l i n e system.
COELACANTH CHARACTERISTICS
b
b
Heavy cosmoid scales
b
Fleshy f i n s
b
Lungs a r e Large s a c - l i k e and f i l l e d w i t h f a t
and connective t i s s u e .
b
Bone has been reduced and replaced w i t h
cartilage.
b
EVOLUTIONARY HISTORY OF THE ACTINOPTERYGIANS
Lack i n t e r n a l n o s t r i l s , t h e nasal sacs a r e
f i l l e d w i t h j e l l y , t h e f u n c t i o n o f which i s
unknown.
I s o l a t e d scales were found i n t h e l a t e S i l u r i a n , w h i l e
the f i r s t body f o s s i l s were found i n t h e Middle
Devonian. The e a r l y f i s h were small, possessing heavy
scales and complex, f u l l y o s s i f i e d s k u l l s ,
characterized by several c i r c u n - o r b i t a l bones. Toothbearing bones characterize both t h e upper and Lower
jaws. The eyes were extremely Large, and t h e mouths
were Long. These f i s h were c h a r a c t e r i z e d by a
heterocercal t a i 1 (possessing an extremely Long upper
Lobe), a s i n g l e dorsal f i n was s i t u a t e d f a r back on the
body. The v e n t r a l surface had an anal f i n a l s o
s i t u a t e d f a r back on t h e body. P e c t o r a l and p e l v i c
f i n s were widely separated. The vertebrae were
incompletely o s s i f i e d and t h e notochord was v e r y
conspicuous.
Heart i s a simple s e r i e s o f Linear chambers.
t
B r a i n case i s Large, but t h e b r a i n w i t h i n i s
v e r y small.
w
No p i n e a l foramen
b
Loss o f s a l t s i s prevented by maintaining a
h i g h osmotic concentration achieved through
r e t e n t i o n o f urea i n t h e blood (a s i m i l a r
mechanism used by sharks).
b
Eggs a r e Large (100 mn) and develop w i t h i n t h e
maternal oviduct (ovoviviparous)
The actinopterygian f i s h were t r a d i t i o n a l l y d i v i d e d
i n t o three groups. Although these groups appear t o
Lack s c i e n t i f i c i n t e g r i t y ( a c l a d i s t would c e r t a i n l y
not recognize them) they do represent stages i n t h e
e v o l u t i o n o f t h i s f i s h group, and t h e r e f o r e I have
r e t a i n t h i s somewhat o l d fashion scheme. The groups
are: b
CHONDROSTEI
(most p r i m i t i v e forms)
b
HOLOSTE I
( i n t e r m e d i a t e forms)
( = NEOPTERYGII)
b
TELEOSTEI
ORDER DIPNOI (Lungfish)
-
Three L i v i n g genera. One genera o c c u r r i n g i n South
America, South A f r i c a and A u s t r a l i a respectively. They
Like t h e Coelacanths share s i m i l a r anatomical features
w i t h t h e amphibians.
CHONDROSTEI
These were abundant i n t h e Palaeozoic and a r e sometimes
r e f e r r e d t o as Palaeoniscoids. They were g e n e r a l l y
small f i s h w i t h u p t i l t e d (heterocercal) t a i l s and
scales covered w i t h ganine ( = ganoid scales).
DIPNOI CHARACTERISTICS
b
Cosmoid scales
b
Fleshy f i n s
b
Reduction i n o s s i f i c a t i o n o f bone
b
Functional Lungs
b
A u s t r a l i a n forms can s u r v i v e i n stagnant water
by a i r - b r e a t h i n g .
The other genera can s u r v i v e
complete d r y i n g up o f the water by burrowing
and a e s t i v a t i n g (dormancy phase). The A f r i c a n
Lungfish a r e so dependent on a i r t h a t i f kept
underwater they w i l l drown.
(most advanced forms)
A great v a r i e t y o f forms e x i s t e d i n t h e Palaeozoic,
ranging from Long t h i n almost e e l - l i k e forms t o
L a t e r a l l y compressed deep-bodied forms (resemble angel
f i s h ) . The group i s g e n e r a l l y e x t i n c t except f o r the
f o l l o w i n g examples.
b
SUBCLASS ACTINOPTERYGII
Sturgeon f i s h jAcipenser) represented by
s i x t e e n species. These have g e n e r a l l y Lost
t h e i r ganoid scales except i n t h e t a i l r e g i o n
and t h e r e have a naked skin. They have
replaced scales w i t h a p a r t i a l covering o f
p l a i n bony plates. The skeleton, although
p r e v i o u s l y o s s i f i e d i s now mostly
cartilaginous.
Paddle f i s h they have a l s o Lost most o f t h e i r
ganoid scales. Their jaws have degenerated and
they tend t o scavenge w i t h t h e i r mouths open.
This i s c u r r e n t l y t h e most nunerous group o f
vertebrates w i t h respect t o nunber o f species and t o t a l
population nunber. From t h e carboniferous time they
have become t h e most dominant f i s h group.
b
These f i s h a r e c h a r a c t e r i z e d by ganoid scales. A
ganoid scale i s formed by p a r a l l e l Layers o f bone,
above t h i s p o r t i o n was middle Layer o f spongy bone
r i c h l y supplied w i t h blood vessels. F i n a l l y there i s an
upper Layer o f hard ganoine formed around numerous p u l p
c a v i t i e s , above which t h e r e i s a t h i n Layer o f enamel.
These are s i m i l a r t o sarcopterygianfs cosmoid scale
except t h e L a t t e r have cosmine r e p l a c i n g ganoine, which
forms a p a r t i c u l a r l y heavy, shiny scale.
B i c h i r (Polypterus) occur i n Central A f r i c a .
These f i s h have a symnetrfcal caudal f i n , a
dorsal f i n t h a t i s s p l i t i n t o a s e r i e s o f s a i l Like structures, and p a i r e d f i n s t h a t resemble
those o f Lobe-fined f i s h . These f i s h a l s o
possess Lungs, and t h e nasal s t r u c t u r e i s
s i m i l a r t o the coelacanths. The scales a r e a
heavy ganoid type. These were o r i g i n a l l y
thought t o belong t o t h e Crossopterygians, but
recent i n t e r p r e t a t i o n i s t h a t they a r e modified
descendants o f the Palaeoniscoids.
HOLOSTEI
Over e v o l u t i o n a r y time t h e a c t i n o p t e r y g i a n f i s h Lost
the various Layers o f t h e scale, w i t h time i t f i n a l l y
came t o c o n s i s t s o f o n l y bone. I n p r i m i t i v e
a c t i n o p t e r y g i a n f i s h t h e r e were f u n c t i o n a l Lungs (and
even i n one L i v i n g f i s h today) but otherwise these have
been m o d i f i e d i n t o h y d r o s t a t i c organs (swim bladders)
which c o n t r o l t h e buoyancy o f t h e animal).
From an
e a r l y stage these f i s h had Large eyes, and probably
.
These were t h e dominant f i s h o f t h e middle Mesozoic.
Some had Long, up-turned s h a r k - l i k e t a i l s . The jaws
became shorter, and t h e scales tended t o Lose t h e i r
ganoid coverings. Most o f t h e r a d i a t i o n was i n t h e
marine environment, and w i t h the f o l l o w i n g exceptions
t h i s group i s e x t i n c t .
Gar pikes (Lepisosteus), these are f a s t
swimning f i s h t h a t are s i m i l a r t o the ancestral
forms, they have elongated jaws and are
associated w i t h a predacious habit.
(m),
these f i s h are more derived ( v i z
Bowfin
less p r i m i t i v e than t h e gar pikes), t h e i r
scales have l o s t t h e i r ganoid covering.
ALL modern Amphibians belong t o the SUBCLASS
LISSAMPHIBIA.
SALAMANDERS (ORDER CAUDATA)
F
Head and neck region d i s t i n c t , t h e trunk Long
and e i t h e r c y l i n d r i c a l o r depressed
dorsoventrally and possess a Long t a i l .
TOADS AND FROGS (ORDER ANURA)
TELEOSTE I
b
.
Originated i n t h e middle t o l a t e Mesozoic. E a r l y forms
s u p e r f i c i a l l y resembled sharks, but t h e i r upturned
shark- 1ike heterocercal t a i 1s became reduced and they
have a symnetric appearance ( t h e v e r t e b r a l axis i s
nevertheless turned upwards). The pectoral f i n s are
positioned high up on t h e l a t e r a l surfaces and t h e
p e l v i c f i n s are positioned f a r forward. The scales
have l o s t a l l o f t h e i r ganoid coverings.
The reasons f o r t h e success o f t h e t e l e o s t f i s h are
locomotion and feeding mechanisms. During the
e v o l u t i o n the jaws became s h o r t e r as the hyomandibular
bone and other elements involved i n the suspension o f
the jaws r o t a t e d t h e i r p o s i t i o n on the b r a i n case. As
t h i s occurred t h e m a x i l l a gradually became f r e e from
the other bones and t h e Lever r o t a t e d about i t s
a n t e r i o r attachment. The r e s u l t o f t h i s i s t h a t the
jaw system became adapted t o almost any type o f d i e t .
Teleosts are t h e most v e r s a t i l e group and comprise over
20 000 species. These animals are able t o adapt t o
eating micro-organisms r i g h t through t o some h i g h l y
predacious forms such as t h e f a s t s w i m i n g tuna f i s h .
We even have f i s h t h a t crawl over mud (mudskippers) and
f l y out o f t h e water ( f l y i n g f i s h ) .
CLASS AMPHIBIA (Frogs,
Several features adapt amphibians f o r t e r r e s t r i a l L i f e
such as legs, Lungs, n o s t r i l s connecting t o the mouth
cavity, and sense organs t h a t can f u n c t i o n i n both
water and a i r .
The t r a n s i t i o n form water t o Land involves the
following:-
b
b
b
b
CAECILIANS, LEGLESS FORMS (ORDER GYMNOPHIONA)
b
Limbless and worm l i k e , w i t h a s k i n containing
many small i n t e r n a l scales.
EXTERNAL FEATURES OF THE ANURAN
Highly vascularized s k i n w i t h many mucous glands, t h i s
maintains a moist body surface f o r cutaneous
respiration. Skin may contain poison glands f o r
protection.
Protection may be associated w i t h aposematic
coloration.
Changes i n c o l o r a t i o n can occur due t o three types o f
chromatophores.
Yellowish hue
Iridophores:
L i g h t r e f l e c t i n g and produce a l i g h t
s c a t t e r i n g (Tyndall Blue) which a c t i n g
with yellow pigments produces a green
coloration.
Melanophores:
These are black pigments under the
iridophores, and causes t h e s k i n t o
darken. When t h e melanin granules move
outward they obscure t h e iridophores.
toads, sa lamanders .?i caeci 1ians)
I n t h e l a t e Palaeozoic amphibians f l o u r i s h e d
(Carboniferous t o e a r l y Permian). E a r l y amphibians
were put i n t o a subclass Lepospondyli, and were f a i r l y
small and s i m i l a r t o modern salamanders. This group
even includes forms t h a t have reverted t o l o s i n g t h e i r
Limbs. Another group o f amphibians became very Large
animals (up t o 3 m i n length and were c a l l e d
Labyrinthodonts), and were probably ancestral t o t h e
amphibians o f today. The most p r i m i t i v e f o s s i l
amphibians c e r t a i n l y belong t o t h e Subclass
Labyrinthodontia and include an animal c a l l e d
Ichthyostegalia, f o s s i l s o f which were found i n
Greenland. These animals possessed a Long f i s h - l i k e
t a i l and were very s i m i l a r t o t h e Crossopterygian fish,
except they were t h e f i r s t amphibian t o walk on Land.
b
Head and trunk are joined i n a broad depressed
body, with no neck o r t a i l , s h o r t forelimbs,
Long h i n d limbs and exposed ear druns.
M o d i f i c a t i o n f o r t r a v e l , p l u s maintaining
swimning.
Change i n s k i n t o f a c i l i t a t e respiration.
Replace g i l l s with lungs
Changes i n t h e c i r c u l a t i o n system permits
r e s p i r a t i o n by lungs and skin.
Sense organs t h a t are Land/water compatible.
Larvae o f the amphibian such as t h e frogs have m u l t i p l e
a o r t i c arches as i n fishes. A f t e r metamorphosis they
Lose a l l but one p a i r o f arches. The amphibian s k u l l
i s much less complex than t h a t o f t h e f i s h and possess
fewer bones. The l i m b muscles become more complex i n
.
the a d u l t frog.
The p i t u i t a r y hormone INTERMEDIN causes dispersal o f
the melanin and c o n t r a c t i o n o f t h e iridophores.
VERTEBRA
Up t o 100 i n t h e anurans
250 i n t h e c a e c i l i a n s
PELVIC GIRDLE
Well developed i n the anurans
Less w e l l developed i n t h e salamanders
Without g i r d l e and Limbs i n c a e c i l i a n s
Most amphibians have f i n e t e e t h (upper jaw and roof o f
mouth) and a long prehensile tongue which i s s i t u a t e d
as f a r forward as possible.
Segmented muscles are conspicuous on t h e trunk and t a i l
i n t h e Salamanders and i n t h e trunk o f t h e Caecilians.
G i l l bearing species have special muscles t o move the
g i l l s and open o r close t h e g i l l s l i t s .
RESPIRATION
b
Have the most nunber o f techniques f o r
r e s p i r a t i o n o f a l l vertebrates. This r e f l e c t s
the t r a n s i t i o n from aquatic t o t e r r e s t r i a l
conditions. The f o l l o w i n g are used f o r
respiration:- g i l l s , skin, Lungs, buccopharynx,
and may operate separately o r i n conjunction
with each other.
w
The heart i n f r o g Larvae i s f i s h l i k e w i t h one
atrium and a v e n t r i c l e : i t receives only
directly to
unoxygenated blood which i s pu@
the g i 11s.
Adults have two a t r i u m and one v e n t r i c l e . The
l e f t a t r i u m receives oxygenated blood from the
s k i n and Lungs, t h e r i g h t unoxygenated blood
from t h e general c i r c u l a t i o n .
Despite t h e s i n g l e v e n t r i c l e there i s some
separation o f a t r i a l blood: t h a t sent t o the
r e s p i r a t o r y surfaces i s almost a l l
unoxygenated.
Three p a i r s o f external g i l l s occur i n most
embryos and Larvae but p e r s i s t only i n those
a d u l t forms t h a t are s t r i c t l y aquatic (u.
Sa lamander)
I n Larval tadpoles water i s drawn i n through
t h e mouth and n o s t r i l s and i s then forced over
t h e g i l l s and out through the spiracles.
I n salamanders they a i d t h e i r r e s p i r a t i o n by
moving t h e i r g i l l s .
(u
frogs) have
Those amphibians w i t h Lungs
few i n t e r n a l p a r t i t i o n s t h a t are vascularized.
Consequently t h e Lungs are not very e f f i c i e n t .
I n aquatic species lungs serve as h y d r o s t a t i c
organs being i n f l a t e d when the animals are
f l o a t i n g ( t h e r e i s Lung reduction i n some
Salamanders).
The s k i n o f a l l amphibians i s h i g h l y
vascularized and t h i s permits some aquatic
species t o remain submerged f o r Long periods
and even hibernate i n ponds.
b
Many species have buccopharyngeal respiration;
p u l s a t i o n s o f the t h r o a t move a i r i n and out o f
t h e mouth c a v i t y and aeration o f the blood
occurs i n vessels i n t h e mucous membrane.
REPRODUCTION
b
Mating u s u a l l y occurs i n t h e water, w i t h
external f e r t i l i z a t i o n ( f r o g s and toads).
eggs a r e deposited and grow u n t i l they
metamorphose i n t o the a d u l t stages.
The
The male enters t h e water, clasps the female,
and as the female extrudes her eggs the male
discharges sperm over them.
Some Salamanders have elaborate courtship
where t h e male deposits a gelatinous
spermatophore on t h e bottom o f the stream. The
spermatophore i s taken i n t o t h e female cloaca
where t h e spermatozoa are stored i n the seminal
receptacle and are f e r t i l i z e d ( i n t e r n a l l y ) a t a
l a t e r stage.
b
The amphibian eggs are covered i n a gelatinous
coating, w i t h a d i s t i n c t i v e form o f egg mass
and j e l l y coating.
LARVAE
b
Salamanders resemble t h e i r parents i n general
form.
b
Larvae o f toads and f r o g s are the f a m i l i a r
tadpole which i n i t i a l l y has external g i l l s ,
which are then replaced by i n t e r n a l g i l l s .
Limbs develop a t a Later stage. The mouth i s
horny w i t h Labial t e e t h i s sued t o scrape food
material. The i n t e s t i n e i s Long and slender.
METAMORPHOSIS INVOLVES
I'
Growth o f a wide mouth, loss o f horny jaws and
thedevelopmentofconicalteeth.
Loss o f g i l l s , closure o f g i l l s l i t s and
development o f lungs.
3)
Development o f t h e p r o t r u s i b l e tongue.
4)
Emergence o f t h e f o u r Limbs ( p a i r e d
appendages).
5,
Reduction i n Length o f t h e i n t e s t i n e from Long
herbivore type t o short carnivore type.
6)
Re-absorption o f t a i l and median f i n s .
7)
Biochemical changes include a change i n the
excretory products from t o x i c amnonia t o less
t o x i c urea. A change i n t h e capacity o f t h e
blood t o release oxygen t o t h e tissues, an
adaptation r e f l e c t i n g a more a c t i v e L i f e s t y l e .
The carnivorous d i e t requires t h a t p r o t e i n
d i g e s t i o n be more important (achieved by
increased pepsin and t r y p s i n action). Other
enzymes are secreted which are responsible f o r
the reabsorption o f t h e t a i l .
T i p o f the snout has two small v a l v u l a r
n o s t r i 1s
CLASS REPTILIA
These include the f o l l o w i n g L i v i n g ORDERS:Lizards & snakes
Turtles & tortoises
Crocodiles & a l l i g a t o r s
Tuatara (Sphenodon)
Eyes are Large and Lateral (upper and Lower
eyelids) and a transparent n i c t i t a t i n g membrane
ORDER SQUAMATA
ORDER CHELONIA
ORDER CROCODILIA
ORDER RHYNCHOCEPHALIA
There are some t e n orders o f r e p t i l e s t h a t are e x t i n c t
and they include animals such as t h e dinosaurs and the
pterosaurs ( t h e f l y i n g forms).
Opening t o the ears i s behind t h e eye and under
a moveable f l a p
b
The vent i s i n t h e form o f a Longitudinal s l i t
behind the base o f the h i n d Limbs.
BODY COVERING
These were t h e f i r s t group o f vertebrates adapted f o r
l i f e i n d r y places. Their d r y horny s k i n and scales
r e s i s t Loss o f moisture.
b
Horny scales arranged i n transverse and
Lengthwise rows.
GENERAL CHARACTERISTICS
b
Adult crocodiles have an almost ttexoskeletontt
o f separate bony dermal p l a t e s (osteoderms)
under the dorsal scales i n t h e r e g i o n o f t h e
neck t o the t a i l . These are rectangular o r
oval and o f t e n p i t t e d and some have a median
keel. There are two p a i r s o f epidermal musk
glands.
1)
Body i s covered w i t h d r y c o r n i f i e d s k i n w i t h
scales o r scutes, there are few surface glands.
Two p a i r s o f limbs each t y p i c a l l y w i t h f i v e
toes ending i n horny claws. They are s u i t e d
f o r running, crawling o r climbing.
Limbs may
a l s o be paddle-shaped as i n marine t u r t l e s and
are reduced i n some Lizards, and are absent i n
t h e snakes.
3)
The skeleton i s completely o s s i f i e d .
4)
The heart i s i m p e r f e c t l y four chambered, there
are two a t r i a and a p a r t l y d i v i d e d v e n t r i c l e
( t h e v e n t r i c l e s i n crocodiles i s completely
divided)
')
Respiration i s v i a lungs; pharyngeal and
cloaca1 r e s p i r a t i o n occurs i n some aquatic
turtles.
6
Twelves p a i r s o f c r a n i a l nerves
7)
The body temperature i n Living forms i s
variable (poikilothermic)
*)
F e r t i l i z a t i o n i s i n t e r n a l v i a copulatory
organs; t h e eggs are Large with much y o l k and
have e i t h e r a Leathery o r Limy s h e l l (may be
r e t a i n e d i n body o f some snakes and Lizards
u n t i l the young hatch from t h e i r eggs)
SKELETON
b
Massive s k u l l , w i t h pronounced reduction i n the
nunber o f bones.
b
The long Lower jaw a r t i c u l a t e s a t each s i d e o f
the p o s t e r i o r margin o f the s k u l l on the
quadrat bone. The v e n t r a l surface o f the
cranium i s the Long hard p a l a t e above which are
the r e s p i r a t o r y passages.
The v e r t e b r a l c o l m consists o f
9
10
5
2
+39
b
9,
Segmentation i s meroblastic; and eggs have an
amnion, chorion, y o l k sac and a l l a n t o i s . The
young when they hatch, resemble t h e adults with
no metamorphosis.
b
b
b
b
Dry s k i n
Limbs which permit r a p i d running locomotion.
Greater separation o f oxygenated and
unoxygenated blood.
Complete o s s i f i c a t i o n o f the skeleton.
Eggs s u i t e d t o development on Land w i t h
membrane and s h e l l s t o p r o t e c t the embryo
Between the stermm and t h e pubic bones there
are seven p a i r s o f V shaped abdominal r i b s .
MUSCULAR SYSTEM
b
Muscles o f the head, neck and Limbs are w e l l
d i f f e r e n t i a t e d , though not as c l e a r l y
d i f f e r e n t i a t e d as i n mamnals.
DIGESTIVE SYSTEM
•
Buccal cavity, Large mouth, stout,
unspecialized teeth ( f o r offence and defence)
b
F l a t tongue
b
Oesophagus: slender tube
b
Stomach: large spherical d i v i d e d i n t o fundus
and p y l o r i c p o r t i o n s
b
Coiled small i n t e s t i n e
b
Larger rectun
b
Cloaca and vent
b
Accessory organs t o t h e stomach are t h e Liver
with two Lobes which Lie a n t e r i o r t o the
stomach and a pancreas which l i e s i n the f i r s t
duodenal Loop.
ADVANCES OVER AMPHIBIANS
b
Cervical vertebrae (short 8 f r e e r i b s )
Thoracic vertebrae (connected t o sternum)
Lunbar vertebrae
Sacral vertebrae
Caudal vertebrae
REPTILES ARE NOT AS ADVANCED AS MAMMALS
b
b
b
Lack i n s u l a t e d body coverings
No i n t e r n a l r e g u l a t i o n o f body temperature
True i n t e r n a l development o f embryo does not
occur (eggs are simply retained i n the oviduct)
EXTERNAL FEATURES: THE CROCODILE
b
b
Head, neck, trunk and t a i l are c l e a r l y
discernable.
CIRCULATORY SYSTEM
Long mouth and c o n i c a l teeth set i n sockets.
b
Heart comprises a small sinus venosus, two
a t r i a and two v e n t r i c l e s .
From blood t r a v e l l i n g i n t h e veins i t enters
the sinus venosus -r r i g h t v e n t r i c l e + pulmonary
a r t e r y + lungs -r pulmonary veins + l e f t atrium
-r L e f t v e n t r i c l e + emerges as a p a i r o f a o r t i c
arches.
ARTERIAL SYSTEM
Carotid arteries
Subclavian
-r
-r
SOME CHARACTERISTICS OF OTHER LIVING REPTILES
SCALES
b
neck & head
forelimbs
A o r t i c arch 8 dorsal aorta
cavity
-r
body
COLORATION
VENOUS SYSTEM
b
A n t e r i o r vena cava
C o l l e c t s from
neck, head 8
forelimbs
+
reproductive
organs 8
kidney
Single mid dorsal +
p o s t e r i o r vena cava
Hepatic p o r t a l
+
digestive
tract
TURTLES AND TORTOISES
RESPIRATORY SYSTEM
Paired n o s t r i l s
I n t e r n a l nares
P a l a t i n e valve, prevents water entering
Glottis
Larynx ( c a r t i l a g i n o u s w i t h p a i r e d vocal cords)
Tubular trachea r e i n f o r c e d w i t h c a r t i l a g e
Divides i n t o two short bronchi
Lungs spongy w i t h greater p a r t i t i o n i n g
+
ureter
+
cloaca
NERVOUS SYSTEM/SENSE ORGANS
F
Two o l f a c t o r y Lobes connected t o t h e large
cerebral hemisphere
b
Two oval o p t i c Lobes
F
Median pear-shaped cerebellun
b
Medulla oblongata spread L a t e r a l l y
F
Narrows i n t o a s p i n a l cord
F
V e n t r a l l y between t h e bases o f t h e cerebral
hemi sphere are t h e o p t i c t racts/opt ic nerves,
infundibulum and hypophysis, twelve p a i r s o f
c r a n i a l nerves and p a i r e d spinal nerves.
Oval s h e l l composed o f p l a t e - l i k e bones w i t h a
d e f i n i t e p a t t e r n sutured together with dense
connective tissue. Dorsal surface i s r e f e r r e d
t o as a carapace and the v e n t r a l surface i s
r e f e r r e d t o as t h e plastron. S o f t - s h e l l e d
t u r t l e s have a Leathery carapace. The jaws
lack teeth and bear c o r n i f i e d b e a k - l i k e
structures t o cut/tear/crush vegetation.
SPHENODON (TUATARA)
b
EXCRETORY SYSTEM
Two f l a t l o b u l a r kidneys
Reptiles can a l s o have some very d i s t i n c t i v e
colour patterns. The chromatophores (pigments)
resemble those o f t h e amphibians w i t h X
(ye1 low), iridophores (bluish/white) and dark
rnelanophores. Colour changes are under
hormonal c o n t r o l o f intermedin.
SOME LIVING REPTILE GROUPS
b
b
Modified i n a v a r i e t y o f ways such as t h e
minute scales on t h e f e e t o f geckoes which
allow them t o climb smooth surfaces. Marine
iguanas have a c r e s t o f Long scales on t h e i r
backs. Chameleons have scales formed i n t o long
horns and the A u s t r a l i a n thorny d e v i l has
scales modified i n t o thorns f o r protection.
L i z a r d - l i k e animal but very much more
p r i m i t i v e , found o n l y i n New Zealand. Has a
median pineal eye and no copulatory organs.
LIZARDS
b
Varied body shapes. Limbs can be long, short,
v e s t i g i a l (reduced) o r absent. The t a i l
vertebrae i n some species may be incompletely
o s s i f i e d and i f the t a i l i s seized by a
predator the vertebrae separates a t these
breaking p o i n t s and the t a i l i s broken o f f .
Lost t a i l p a r t s can be regenerated.
SNAKES
b
SENSES INCLUDE
b
Taste buds on the tongue
b
O l f a c t o r y c e l l s i n nose
b
Eyes (colour v i s i o n ) w i t h Lachrymal glands
b
Ears short external a u d i t o r y canal, tympanic
membrane, middle ear houses one ear bone
(stapes) and the inner ear consists o f three
semicircular canals
REPRODUCTIVE SYSTEM
b
Paired gonads
b
Mature male has two round testes, a ductus
deferens and a s i n g l e median penis
b
Mature female has two ovaries, an open funnel
o f t h e oviduct running t o the cloaca
Characterized by a loss o f appendages and
extreme elongation. Vestiges o f the p e l v i c
g i r d l e and h i n d Limbs p e r s i s t i n boas, pythons
etc. Most snakes, however, lack Limb girdles,
sternum, eyelids, external ear openings and a
bladder.
Snakes are characterized by nunerous vertebrae
(200 t o 4001, many slender segmented body
muscles connect t h e vertebrae t o vertebrae, the
r i b s t o vertebrae and t h e r i b s t o t h e r i b s .
Locomotion without Limbs i s achieved by
backward pressure o f t h e Lateral Loops o f t h e
body against surface i r r e g u l a r i t i e s . Snakes
can t r a v e l i n s t r a i g h t l i n e s by h i t c h i n g scales
against t h e ground surface.
Snakes can ingest whole, Large-sized prey
items. This i s achieved through modifications
t o the jaw.
This m o d i f i c a t i o n s include two
mandibles connected w i t h f l e x i b l e connective
tissue, loose attachment o f other jaw bones
(quadrate) and movement o f the bones o f the
p a l a t e and slender backward p o i n t i n g teeth. I n
e f f e c t the snake i s able t o d i s l o c a t e i t s Lower
jaw t o increase i t s gape size.
hopping, running, climbing o r swirmning. The
upper segments o f t h e h i n d Limb are muscular,
whereas the slender lower legs o r shanks
contain tendons, w i t h L i t t l e muscle and
sheathed i n c o r n i f i e d scales, as are the f o u r
toes which end i n horny claws.
CLASS AVES
CHARACTERISTICS
.
b
b
b
b
b
b
b
b
Body covered with feathers
Two p a i r s o f limbs; a n t e r i o r limbs modified f o r
f l i g h t , p o s t e r i o r adapted f o r perching, walking
o r swimming. Each f o o t i s u s u a l l y equipped
w i t h f o u r toes sheathed w i t h c o r n i f i e d skin.
Skeleton, t h i n - w a l l e d bones but possessing
great s t r u c t u r a l strength, f u l l y ossified,
mouth possessing a p r o j e c t i n g beak o r b i l l made
from k e r a t i n i z e d t i s s u e w i t h a horny sheath and
teeth are absent, s k u l l w i t h one o c c i p i t a l
condyle, neck very f l e x i b l e , p e l v i s fused,
sternum enlarged and u s u a l l y possessing a
median keel, t a i l vertebrae fused and
compressed p o s t e r i o r l y .
Heart f o u r chambered (two a t r i a and two
separate v e n t r i c l e s ) ; o n l y t h e r i g h t a o r t l c
arch persists; red blood c e l l s are nucleated,
oval and biconvex.
Respiration i s by way o f compact Lungs attached
t o r i b s and connected t o t h i n - w a l l e d a i r sacs
extending between i n t e r n a l organs, voice formed
from t h e s y r i n x a t the base o f t h e trachea.
No o r d i n a r y bladder, e x c r e t i o n i n semi s o l i d
form ( u r i c acid; females u s u a l l y only have the
L e f t ovary and oviduct.
Twelve p a i r s o f c r a n i a l nerves
Body temperature i n t e r n a l l y regulated
(homeothermy)
F e r t i l i z a t i o n i n t e r n a l , eggs with large yolk,
covered w i t h a hard Limy s h e l l and deposited
e x t e r n a l l y f o r incubation. C e l l d i v i s i o n i s
meroblastic and embryonic membranes (amnion,
chorion, y o l k sac and a l l a n t o i s ) present during
development w i t h i n t h e egg. Young hatchlings
are cared f o r and feed by parents.
F
b
BODY COVERING
b
b
b
b
b
b
b
b
Insulated body coverings.
Complete separation o f venous and a r t e r i a l .
c i r c u l a t i o n i n the heart.
Regulated body temperature.
High r a t e o f metabolic a c t i v i t y
Ability to f l y
Specialized care f o r young.
b
b
body covering not o f h a i r
mode o f reproduction very d i f f e r e n t
t h e i r a b i l i t y t o f l y (Limited t o bats i n t h e
case o f mamnals)
D i s t i n c t head, long f l e x i b l e neck, a stout
spindle-shaped body o r trunk.
b
The mouth i s extended as a pointed biLl/beak
w i t h a horny covering. On the upper mandible
are two s l i t - l i k e n o s t r i l s
b
The eyes a r e Large and Lateral, each w i t h an
upper and Lower eyelid. Beneath there i s a
n i c t i t a t i n g membrane, which can be drawn
independently across the eyeball from the
a n t e r i o r corner.
b
Below and behind each eye i s an ear opening,
hidden under special feathers.
The base o f t h i s feather bud sinks i n t o a
c i r c u l a r depression: t h e f u t u r e f o l l i c l e .
The outermost epidermal c e l l s on the bud become
a smooth c o r n i f i e d sheath (periderm): other
epidermal c e l l s become arranged i n p a r a l l e l
ribs, a Large median one forming the f u t u r e
shaft, the others producing barbs.
CONTOUR FEATHERS
b
The external covering and includes t h e enlarged
f l i g h t feathers o f the wings and t a i l .
b
Consists o f a vane, c e n t r a l shaft, a hollow
q u i l l attaching t o the f o l l i c l e . Each h a l f o f
the vane i s composed o f many narrow p a r a l l e l
and c l o s e l y spaced barbs j o i n i n g t h e sides o f
t h e shaft.
EXTERNAL FEATURES
b
Begins Like the scale o f a r e p t i l e : v i z as a
Local dermal p a p i l l a t h r u s t i n g up t h e o v e r l y i n g
epidermis.
The c e n t r a l s o f t , dermal p u l p ( o r i g i n a l dermal
p a p i l l a ) contains t h e blood vessels and i s
wholly n u t r i t i v e , d r y i n g on completion o f
growth, so t h a t the feather i s p u r e l y an
epidermal structure. The pigments f o r
c o l o r a t i o n are deposited i n c e l l s when t h e
growth i s completed, t h e sheath breaks and
crumbles away o r i s removed by preening.
Birds are notably d i f f e r e n t from mamnals i n
b
D i s t i n c t i v e epidermal structures. They are
Lightweight, f l e x i b l e but r e s i l i e n t body
coverings and create a i r pockets which
insulates t h e body covering, p r o t e c t s the s k i n
and creates wings and t a i l f o r support i n
flight.
THE GROUTH OF A FEATHER
b
b
The s o f t f l e x i b l e s k i n i s Loosely attached t o
t h e muscles beneath. I t Lacks glands except
f o r the o i l gland above the base o f t h e t a i l .
This gland secretes an o i l y substances f o r
I1dressingl1the feathers and keep t h e b i 11 from
becoming b r i t t l e . The feathers grow from
f o l l i c l e s i n the skin.
FEATHERS
Birds represent s i g n i f i c a n t advances
b
The short t a i l bears a f a n - l i k e group o f Longt a i l feathers.
On the proximal and d i s t a l s i d e o f each barb
are numerous smaller, p a r a l l e l barbules, these
are provided w i t h minute b a r b i c e l s o r hooklets,
serving t o h o l d opposing rows o f barbules
Loosely together.
DOWN FEATHERS
b
b
The two forelimbs are modified i n t o wings and
are attached high-up on the back and have long
f l i g h t feathers. The wings are folded i n t o a Z
shape formation a t r e s t and are extended i n
flight.
The h i n d Limbs are generally adapted t o bipedal
b
Young chicks and other hatchlings are covered
p r o v i d i n g excellent
with s o f t downy plunage
insulation.
b
Down feathers have short q u i l l s , reduced s h a f t s
and a Long f l e x i b l e barb w i t h a short barbules.
b
Down i s a l s o present beneath t h e contour
feathers on ducks and other water b i r d s .
-
r i g i d support f o r f l i g h t and permits a s l i g h t
expansion/contraction f o r r e s p i r a t i o n .
FILOPLUMES
b
Minute, h a i r l i k e feathers, sparsely d i s t r i b u t e d
over the body.
b
Grow i n c l u s t e r s near t h e f o l l i c l e s o f some
contour feathers.
b
Each has a Long t h r e a d l i k e shaft w i t h a few
week barbs and barbules a t the t i p .
The r i b s are l a t e r a l and t h e sternun i s v e n t r a l
w i t h a Large median keel below which t h e
pectoral muscles attach.
Each thoracic r i b has a d i s t i n c t v e r t e b r a l and
s t e r n a l part, t h e two j o i n i n g n e a r l y a t a r i g h t
angle. The f i r s t f o u r o r f i v e t h o r a c i c r i b s
has a p o s t e r i o r f l a t process overlapping t h e
r i b s behind t o strengthen t h e thorax.
BRISTLES
b
The pectoral g i r d l e consists o f a sword-like
scapula Lying p a r a l l e l t o the vertebrae and
over the r i b s . The coracoid bone occurs
between the scapula and the sternun.
Some b i r d s have h a i r - l i k e growths t h a t are
modified feathers, each w i t h a short q u i l l and
a slender s h a f t w i t h a few v e s t i g i a l barbs a t
t h e base. These a r e seen about t h e mouths o f
some b i r d s such as f l y c a t c h e r s and serve a
t a c t i l e function.
C l a v i c l e hanging v e n t r a l l y from t h e scapula:
the two c l a v i c l e s are fused a t t h e i r v e n t r a l
ends t o form the I1Vl1 shaped f u r c u l a (wishbone)
attaching t o t h e sternun.
FEATHER COLORATION/PATTERNING/MOULT
b
Feather's colour r e s u l t ' s c h i e f l y from pigment
deposition during growth.
b
Iridescence i s due t o microscopic, t h i n p l a t e s
on t h e surface s t r u c t u r e o f feathers.
b
Feathers o n l y grow i n defined areas c a l l e d
feather t r a c t s .
b
Feather replacement i s c a l l e d moult, and i s
u s u a l l y an o r d e r l y gradual process. Large
feathers on t h e wing are moulted i n syrrmetrical
p a i r s so t h a t f l i g h t i s not hindered. Ducks
and Penguins moult a l l o f t h e i r feathers
simultaneously, and they are f l i g h t l e s s u n t i l
t h e replacements grow in.
The scapula, coracoid and c l a v i c l e meet
d o r s a l l y t o form a c i r c u l a r canal as a p u l l e y
f o r the tendon.
Each forelimb i s attached high on t h e dorsal
surface: the humerus p i v o t i n g i n t h e glenoid
fossa on t h e coracoid.
The fore-arm contains t h e radius and t h e ulna
as i n other Land vertebrates, but other wing
bones are modified t o promote a s t a b l e support
f o r the f l i g h t feathers.
There are two carpels and three d i g i t s .
-
Other carpels are fused t o t h e metacarpals t o
form the carpometacarpus
SKELETON
b
D e l i c a t e compared t o t h a t o f mamnals.
b
Many o f t h e bones possess c a v i t i e s t o Lessen
t h e i r weight. The skeleton i s modified f o r
f l i g h t , f o r bipedal Locomotion, and t h e Laying
o f r e l a t i v e l y Large eggs w i t h hard shells.
- t h e second d i g i t bears the a l u l a
- two
the t h i r d d i g i t i s t h e longest (composed o f
segments)
-
Bones o f t h e cranium are separate i n young, krt
are fused i n a d u l t s (except f o r t h e nasal
f r o n t a l hinge which permits s l i g h t movement o f
t h e upper jaw).
The p r i n c i p a l f l i g h t feathers (primaries) are
supported on d i g i t s three and f o u r and on the
carpometacarpus.
The braincase i s rounded, Large o r b i t s occur
f o r t h e eye. Jaws formed by (premaxi llae,
maxi 1l a e and mandibles) p r o j e c t forward o f the
bony beak.
The secondary f l i g h t feathers are supported on
the ulna
The t e r t i a r y f l i g h t feathers are supported on
the humerus.
Lower jaws hinge on the moveable quadrate
connecting t o t h e squamosal bone. The s k u l l
a r t i c u l a t e s on a s i n g l e o c c i p i t a l condyle with
t h e f i r s t neck vertebrae.
The p e l v i c g i r d l e i s broad: u n i t e d w i t h a
synsacrum, t h a t i s widely opened v e n t r a l l y ,
p e r m i t t i n g the passage o f large eggs.
16 c e r v i c a l vertebrae (neck) each i s saddle
shaped and permits f r e e movement o f the neck
f o r feeding and preening.
The trunk vertebrae are c l o s e l y f i t t i n g , they
have r i b a r t i c u l a t i o n s t h a t are Lateral i n t h e
thorax region, but are otherwise fused i n t o a
s o l i d synsarcun t o which the p e l v i s i s
attached.
the f o u r t h d i g i t i s t h e innermost (composed
o f a s i n g l e segments)
The p e l v i c g i r d l e consists o f an a n t e r i o r
iliun, a p o s t e r i o r ischiun, a slender v e n t r a l
pubis where these three bones meet, and a
socket where the acetabulun receives the head
o f the femur.
b
The Leg consists o f a
-- Tibiotarsus
Femur
-
No Lumbar region i s evident.
-
Four f r e e caudal vertebrae.
-
Compressed terminal pygostyle (fused) permits
movement o f t h e t a i l .
SLender/incomplete F i b u l a
Fused tarsometatarsus
Patella: h e l d i n Ligaments before femurtibiotarsal
Four toes: three i n f r o n t and one behind.
MUSCULAR SYSTEM
A Large t h o r a c i c c a v i t y formed from r i b s which
p r o t e c t s t h e i n t e r n a l organs and provides a
b
Lower vertebrates have dominance o f segmented
a r t e r i e s each w i t h three l a r g e branches: the
c a r o t i d t o t h e head/neck, t h e branchial t o the
wing and t h e pectoral t o t h e breast. The arch
continues as the dorsal aorta supplying t h e
r e s t o f the body.
over non-segmented muscles.
B i r d s and mamnals have a greater proportion o f
non-segmented muscles. The Large pectoral
muscles which o r i g i n a t e on the outer side o f
t h e s t e r n a l keel and i n s e r t s on t h e
v e n t r o l a t e r a l head o f t h e humerus.
A h e p a t i c - p o r t a l system exists.
t
I n other Land vertebrates the forelimb i s
r a i s e d by muscles on the dorsal surface, but i n
b i r d s such movement i s due t o a v e n t r a l muscle
c a l l e d t h e supracoracoideus.
t
N o s t r i l s : connected t o i n t e r n a l nares and a
slit-like glottis
t
Trachea: r e i n f o r c e d w i t h h o o p - l i k e c a r t i l a g e
that i s p a r t l y calcified.
t
Syrinx: possess vocal muscles.
b
Bronchus: 4 lungs which are small
interconnecting chambers t h a t opening i n t o
Larger chambers c a l l e d the Parabronchi which
comnunicate with t h e bronchi and a i r sacs which
extend between organs i n t h e body c a v i t y and
space around t h e neck vertebrae and i n t o t h e
Larger bones.
RESPIRATORY SYSTEM
-
supracoracoideus o r i g i n a t e s on t h e keel and
tapers t o a strong tendon.
The muscles o f t h e femur and t h e t i b i o t a r s u s
are used f o r running and perching.
The shank and f e e t c o n t a i n l i t t l e muscle: an
adaptation t o reduce heat Loss.
Toes are moved by tendons t h a t are connected t o
muscles i n the upper segments o f the Legs.
Tendons move through spaces Lubricated by
fluid.
- Air
i s brought i n by movement o f muscles
between the r i b s bowing L a t e r a l l y and by
abdominal muscle.
DIGESTIVE SYSTEM
-
A renal p o r t a l system i s reduced.
The c o n t r a c t i o n o f t h e pectoral muscle moves
t h e wing downwards and l i f t s the b i r d 1 s body i n
flight.
- Contraction o f
t
Tongue, small and pointed with horny covering
-
w
Mouth c a v i t y : roofed w i t h Long p a l a t a l f o l d s
t
Short pharynx
-
t
Tukrlar/muscular oesophagus
t
Stomach: s o f t a n t e r i o r proventriculus
t
Disk shaped v e n t r i c u l u s o r gizzard + walls o f
Lined i n t e r n a l l y by
t h i c k , dense musculature
e p i t h e l i a l s e c r e t i o n -, food ground up by a c t i o n
o f muscular w a l l and w i t h gravel/stones g&
which f u n c t i o n as teeth.
t
-
-
I n t e s t i n e i s slender and consists o f several
c o i l s o f the Large rectum a t t h e junction o f
the two caeca o r b l i n d pouches.
t
Cloaca: d o r s a l l y bears an outgrouth: t h e Bursa
o f Fabricus.
t
Large r e d Liver i s b i - l o b e d w i t h a g a l l bladder
and two b i l e ducts.
t
Pancreas: three ducts discharge i n t o t h e
a n t e r i o r Loop o f t h e i n t e s t i n e .
HEART
t
-
-
t h e thorax reverse t h e flow.
On i n s p i r a t i o n a i r enters the bronchus, by
passes t h e Lungs and enters the p o s t e r i o r a i r
sac.
On expiration, i t flows i n t o t h e small Lungs.
Upon the next i n s p i r a t i o n a i r w i l l f i l l the
p o s t e r i o r a i r sacs, t h e f i r s t a i r w i l l pass
from the Lungs t o the a n t e r i o r sacs.
U i t h e x p i r a t i o n a i r i n t h e a n t e r i o r sac i s
expelled i n t o the bronchus and t o t h e outside
through the mouth.
I n t h i s way a one-way flow o f a i r i s
maintained through t h e Lungs. The d i r e c t i o n
o f a i r i s opposite t o t h a t o f blood c r e a t i n g
a counter-current system.
A i r sacs may a l s o d i s s i p a t e heat generated
through the muscular contractions.
EXCRETORY SYSTEM
t
Paired kidneys: three-lobed and attached
d o r s a l l y under t h e p e l v i s .
t
From each i s a slender u r e t e r which extends
p o s t e r i o r l y t o the dorsal w a l l o f the cloaca.
t
No bladder
t
Semi-solid nitrogenous waste ( u r i c acid) pass
down the u r e t e r s and out o f the cloaca v i a the
vent.
NERVOUS SYSTEM AND SENSE ORGANS
Four chambered, two t h i n - w a l l e d a t r i a and two
t h i c k walled v e n t r i c l e s .
Proportionately larger than r e p t i l e s .
t
O l f a c t o r y lobes are small (poor sense o f
smell).
t
Cerebral hemispheres a r e l a r g e and smooth.
Completely separate venous/arterial
bloodstreams.
Sinus venosus i s incorporated i n t h e r i g h t
atriun.
Blood from two precaval and one post caval
enters t h e r i g h t atrium -, r i g h t v e n t r i c l e -,
pulmonary a r t e r y -, c a p i l l a r i e s o f the Lung -,
l1oxygenatedl1 r e t u r n s v i a pulmonary veins t o
L e f t a t r i u m + L e f t v e n t r i c l e -, s i n g l e r i g h t
a o r t i c arch which gives o f f two innominate
Optic lobes on t h e midbrain are w e l l developed.
t
Cerebel lun has an increased surface w i t h many
s u p e r f i c i a l folds.
t
Nerve cord and p a i r e d s p i n a l nerves s i m i l a r t o
other vertebrates.
-
.#
b
The t h o r a c i c o r branchial plexus serves the
Large p e c t o r a l muscles f o r f l i g h t .
s h e l l . The s h e l l i s incubated during growth o f
the embryo.
b-
The eyes are p r o p o r t i o n a t e l y very Large:
phenomenally keen s i g h t . Colour v i s i o n i s
acute and focusing very rapid.
The young hatchlings o f chickens and ducks are
precocia1:- they are well formed and f u l l y
covered w i t h down and are able t o run away
idiately.
b
Hearing i s not as acute as f o r m a m l s .
A short external a u d i t o r y canal
-, leads t o tympanic membrane
-, bone c o l u n e l l a a u r i s which transmits waves
across t h e oval window
-, From t h e middle ear on each s i d e i s a
eustachian tube Leading t o the pharynx with
t h e two having a comnon opening a t the back
o f t h e palate.
-, t h e cochlea o f t h e inner ear i s a short,
blind-ended tube t h a t i s intermediate i n the
developnent between r e p t i l e s and mamnals.
-, Chemoreception (smell and taste) i s u n l i k e l y
t o be w e l l
developed except i n a few cases.
Chicks o f song birds, canaries, pigeons hatch
as b l i n d , naked and helpless and are c a l l e d
a l t r i c i a l chicks.
B i r d s generally have d i f f e r e n t and
c h a r a c t e r i s t i c seasons f o r breeding. Breeding
comnences w i t h a c o u r t s h i p display, defence o f
t e r r i t o r i e s , followed by c o n s t r u c t i o n o f nests,
Laying o f eggs, incubation o f eggs and t h e
caring o f t h e hatchlings.
FLIGHT
b
The shape o f the wings and t h e manner i n which
they are moved r e s u l t s i n forward propulsion
w i t h as L i t t l e expenditure o f energy as
possible.
ENDOCRINE GLAND
b
P i t u i t a r y : below t h e base o f t h e brain.
b
Thyroid: two l a t e r a l Lobes beneath the jugular
and a t t h e o r i g i n where the subclavian and
c a r o t i d meet.
b
The wing i s an a i r f o i l w i t h a Leading edge t h a t
i s t h i c k and a t r a i l i n g edge t h a t i s t h i n .
The upper surface o f t h e wing i s curved
convexly, whereas t h e Lower surface i s s l i g h t l y
concave.
Adrenals: v e n t r a l surface o f t h e kidneys
Pancreas: w i t h i s l e t s o f Langerhans.
n
;.
b
The spindle-shaped stream-lined body r e s u l t s i n
m i n i m a i r resistance.
Consequently a i r passing over t h e curved upper
surface must move f a s t e r than t h e a i r
underneath the wing.
Endocrine secretions o f t h e gonad regulate
plumage).
secondary sexual characters ( s
REPRODUCTIVE SYSTEM
This causes a s l i g h t negative (Low) pressure on
the upper surface i n r e l a t i o n t o t h e lower
surface.
MALE
b
Two oval, w h i t i s h t e s t e s a r i s i n g from each i s a
much convoluted ductus deferens which extends
p o s t e r i o r l y p a r a l l e l t o the ureter. I n many
b i r d s i t i s d i l a t e d as seminal vesicles before
e n t e r i n g cloacal. Some b i r d s have v e s t i g i a l
penis (non-functional).
These d i f f e r e n c e s i n pressure creates an upward
force c a l l e d l i f t (generated by t h e need t o
equalize the pressures on e i t h e r s i d e o f the
wing; since the wing has a h i g h pressure on the
underside and a low pressure on t h e upper
surface, the force generated i s upwards).
During breeding t e s t i s becomes enlarged, sperm
accumulates i n t h e ductus deferens and i s
t r a n s f e r r e d t o t h e cloaca o f the male during
copulation.
By increasing the angle o f attack ( r a i s i n g the
p o s i t i o n o f t h e Leading edge i n r e l a t i o n t o the
t r a i l i n g edge) causes an increased amount o f
L i f t u n t i l a s t a l l i s induced.
FEMALE
b
System develops o n l y on the Left side, t h e
ovary i s ear t h e L e f t kidney: Close by i s t h e
open expanded funnel o r infundibulun o f the
oviduct. The duct extends p o s t e r i o r l y t o the
cloaca.
I n non-laying birds, the ovary i s small
containing minute eggs and the duct i s small.
I n the season o f egg-laying the ovary enlarges,
a mature ovum receives a f u l l quota o f y o l k
before being released. The mature ovum escapes
from t h e ovarian f o l l i c l e i n t o the abdominal
c a v i t y and enters t h e funnel a t the top end o f
t h e oviduct (movement i s by c i l i a t e d
epithelium).
F e r t i l i z a t i o n occurs i n the upper oviduct,
albumen i s added by glands i n the middle
p o r t i o n and t h e s h e l l membranes are secreted by
glands i n t h e p o s t e r i o r part.
REPRODUCTION (BIRDS IN GENERAL)
b
A s t a l l i s where t h e smooth a i r flow i s
disrupted and turbulence i s induced, the r e s u l t
i s t h a t no L i f t now occurs and f l y i n g i s no
Longer possible.
Eggs are l a i d w i t h much y o l k and a hard Limy
U n l i k e a fixed-wing a i r c r a f t , t h e a i r f o i l can
be changed i n b i r d s by muscular actions.
The outerpart o f t h e major f l i g h t feathers
( t r a i l i n g edge) are s e m i f l e x i b l e and can be
separated, c r e a t i n g s l o t s which reduce t h e
turbulence and avoid a s t a l l when there i s a
high angle o f attack. ( s i m i l a r t o f l a p s i n
f i x e d wing a i r c r a f t ) .
b
The shape o f t h e wing i s r e l a t e d t o t h e type o f
f l i g h t . Warm a i r r i s i n g from sun-heated s o i l s
o r rocks provides upward thermals i n which
b i r d s c i r c l e t o maintain p o s i t i o n on the
thermal e.g.vultures. Such b i r d s have broad,
large wings.
Wind deflected upwards by mountains permits a
s i m i l a r soaring p a t t e r n o f f l i g h t .
I n the more usual, h o r i z o n t a l winds, soaring
b i r d s may remain s t a t i o n a r y o r move forward.
B i r d s such as albatrosses soar close over t h e
ocean i n an undulating pattern, r i s i n g against
ever present winds and they use long narrow
wings.
Flapping f l i g h t i s t h e most usual. The wings
are f u l l y spread and swept forward ( a c t i o n o f
t h e p e c t o r a l muscle) and then are p a r t l y folded
f o r t h e recovery s t r o k e t h a t i s upwards and
backwards.
F a i r l y small wing characterize such
fliers.
SUBCLASS PROTOTHERIA
ORDER MONOTREMATA
b
These are the most p r i m i t i v e , s u r v i v i n g mamnals
o f today.
b
The o n l y l i v i n g Order: MONOTREMATA
b
Before hatching t h e embryo l i v e s on t h e y o l k
contained w i t h i n the p l i a b l e egg.
b
A f t e r hatching t h e young are nourished by m i l k
from the mother's m a m r y glands.
CLASS MAMMALIA
b
b
This r e f e r s t o animals possessing mamnary
glands.
b
Mamnals possess body h a i r ( a t sane time i n
t h e i r L i f e h i s t o r y , although t h i s may be
secondarily Lost)
b
They are Homeothermic:- maintaining a constant
body temperature.
b
They are endothermic:- meaning t h a t the heat
f o r maintaining body temperature comes from
t h a t generated w i t h i n the body.
b
M a j o r i t y o f mamnals a r e viviparous, with t h e
young u s u a l l y nourished before b i r t h through a
placenta t h a t attaches t h e embryo t o the
uterus.
*
9
There a r e approximately 4000 L i v i n g species o f
mama ls
.
'
EVOLUTION
b
Evolved from mamnal-like r e p t i l e s (synapsids).
b
The synapsid l i n e eventually Lead t o the
therapsids, one Line o f which were the
theriodonts. The theriodonts were half-way
between a r e p t i l e and a mamnal, and were small
animals occupying s i m i l a r L i f e - s t y l e s t o t h e
modern day shrews.
b
-
The d i s t i n c t i v e mamnalian c h a r a c t e r i s t i c s t h a t
evolved w i t h these e a r l y m a m l s included an
endothermic physiology w i t h associated
homeothermic a t t r i b u t e s such as i n s u l a t i n g
hair, increased c i r c u l a t i o n e f f i c i e n c y , more
e f f e c t i v e Locomotion, v i v i p a r i t y and greater
parental investment i n t h e i r young.
b
With the e x t i n c t i o n o f the dinosaurs 70 m i l l i o n
years ago, many p o t e n t i a l l1nichesl1on Land, sea
and i n t h e a i r were vacated and an explosive
species r a d i a t i o n o f m a m l s followed during
t h e Cenozoic period.
b
The mamnals are d i v i d e d i n t o two L i v i n g
subclasses the P r o t o t h e r i a (egg-laying
p r i m i t i v e mamnals) and the Theria (more modern
viviparous mamnals).
b
The t h e r i a group are diverged i n t o the
Metatheria (pouched o r marsupial animals) and
t h e Eutheria (placental rnamnals).
MAMMAL IA
-
PROTOTHERIA (monotremes)
- THERIA
-- METATHERIA
(marsupial
EUTHERIA (placental)
There are no teats; the young Lap up m i l k as i t
oozes from the tubular glands.
w
There are f i v e L i v i n g species o f spiny anteater
(Echidna) and one species o f d u c k - b i l l e d
platypus (Orni thorhynchus).
b
They Left the main m a m l i a n stock f a r back
the Mesozoic era.
b
The s k u l l has may p r i m i t i v e and/or r e p t i l i a n
features. The vertebra are very Like t h a t o f
r e p t i l e s , e s p e c i a l l y t h e c e r v i c a l vertebrae
which bear separate r i b s as occurred i n the
synapsid r e p t i l e s .
b
The d i f f e r e n t i a t i o n o f t h e atlas, a x i s and
seven c e r v i c a l vertebrae i s t h e Least f o r any
mamnalian group.
b
There are 17 and 16 t h o r a c i c vertebrae f o r t h e
platypus and the spiny anteater respectively.
b
Limbs are supported on p e c t o r a l and p e l v i c
girdles, and more s i m i l a r t o those o f a
r e p t i l e , and have f a r Less muscle than the
average advanced mamnal.
in
Both the platypus and spiny anteater are h i g h l y
specialized animals and have no teeth i n t h e i r
a d u l t phase, t h e r e f o r e we cannot deduce the
primitiveness o f these.
The p a t t e r n o f reproduction i s unique amongst
mamnals and involves Laying o f eggs. The eggs
have undergone p a r t i a l cleavage p r i o r t o being
Laid.
They show the beginning o f t h e process o f
s u b s t i t u t i o n o f post-natal n u t r i t i o n from
ovarian n u t r i t i o n .
Eggs are incubated f o r 10 days. The female
platypus makes long burrows where the nest i s
made. At b i r t h the young rnonotremes possess an
"egg toothr1 a unique character f o r mamnals.
A f t e r incubation and hatching t h e young enter
the pouch and are feed by m i l k . Postnatal care
obviously preceded t h e egg Laying
characteristic.
Both the echidna and t h e platypus produce m i l k
from about 120 Large s p e c i a l i z e d sweat glands
on the v e n t r a l abdomen. The are no ducts
u n i t i n g t h i s secretion. ALL other mamnals have
nipples which do u n i t e such secretions.
Although p r i m i t i v e these animals have h a i r
suggesting that mesozoic mamnals and even
synapsid mamnals had made progress w i t h
temperature regulation.
Although p r i m i t i v e these animals are able t o
regulate t h e i r body temperatures a t around032 0C
i n an ambient temperature range o f 5 t o 30 C.
The epipubic bones are reduced i n t h e f u l l y
quadrupedal t e r r e s t r i a l forms such as the
Tasmanian Wolf.
A curious f e a t u r e found i n monotremes i s a
grooved e r e c t i l e poison spine on t h e tarsus o f
t h e male.
The c i r c u l a t i o n system i s r e l a t i v e l y advanced.
I n conclusion t h e monotremes are mamnals with
respect t o t h e i r brain, h a i r (insulation),
warm-bloodedness, heart, Larynx and diaphragm.
However, they have obvious r e p t i l i a n a f f i n i t i e s
w i t h respect t o t h e i r ovoviviparous
reproduction and t h e i r skeleton.
b
MARSUPIAL REPRODUCTION
b
The p a t t e r n i s very d i f f e r e n t t o t h a t o f
placentals.
›
Pregnancy i s very short, even less than t h e
oestrus cycle. Hormones normally associated
w i t h development during pregnancy o f placentals
can be removed i n marsupial animals without
terminating the pregnancy.
SUBCLASS THERIA
INFRACLASS METATHERIA
ORDER MARSUPIALIA
These are t h e pouched animals and are represented by
some 250 L i v i n g species. Many o f these species show a
strong anatomical resemblance t o placental animals,
except f o r t h e i r mode o f reproduction.
b
b
Marsupials diverged from an e a r l y stage i n the
e v o l u t i o n o f t h e mamnals.
There i s no special imnune suppressant system
p r o t e c t i n g the foetus from t h e mothers
antibodies as has t o occur i n p l a c e n t a l
mamna 1s
.
b
A t h i n s h e l l p r o t e c t s t h e o w n from t h e
responses o f the uterus t o the f a t h e r ' s
antigens. This p r o t e c t i o n i s b r i e f and t h e
young are born w i t h i n 10 t o 12 days o f the
s h e l l breaking down.
b
The L i f e o f t h e mother i s not i n t e r r u p t e d by
any dramatic b i r t h . The young g a i n Less from
the mother before b i r t h than occurs i n
placentals. The marsupial mother r i s k s Less
and r e t a i n s more freedom.
b
A f t e r b i r t h t h e young enjoy Long p r o t e c t i o n i n
the pouch. These young can be e a s i l y abandoned
i f t h e mother i s stressed.
The marsupials p a r a l l e l the adaptive r a d i a t i o n
accomplished elsewhere by t h e placental mamnals
except f o r forms l i k e bats, whales o r seals.
L i k e t h e monotremes many o f t h e i r features are
s p e c i a l i z e d so t h a t they represent not a s i n g l e
stage on t h e way t o the placental evolution,
but a s p e c i a l i z e d s i d e branch.
There are 172 marsupial species i n Australia,
and accounts f o r t h e e n t i r e mamnalian fauna o f
t h i s continent (except f o r aquatic seals and a
species o f b a t ) and t h e monotremes.
There are successful representatives i n North
and South America e.g. opossuns which have
survived i n competition w i t h the placentals.
Although temperature c o n t r o l may be less well
developed than i n the placental animals,
Learning s k i l l s , v i s u a l d i s c r i m i n a t i o n and
problem s o l v i n g i s equal t o t h a t o f s i m i l a r
p l a c e n t a l mamnals.
The s k u l l i s s i m i l a r t o t h a t o f the p r i m i t i v e
placentals such as the insectivores, with a
r a t h e r small craniun. The teeth are not easy
t o i n t e r p r e t t h e primitiveness o f the group.
The i n c i s o r teeth are more nunerous than i n
p l a c e n t a l m a m l s . There are three and four
premolar and molar teeth respectively i n each
s i d e o f t h e upper o r lower jaw whereas i n
p l a c e n t a l there are f o u r and three premolars
and molars respectively. Obviously many forms
have l o s t teeth and t h i s represents the
ancestral condition. The form o f llcuspstt on
the teeth do some primitiveness.
The skeleton i s generally s i m i l a r t o t h a t o f
t h e placentals and has g r e a t l y changed from the
monotremes and the r e p t i l e s . The thoracic
region consists o f 13 p a i r s o f r i b - b e a r i n g
vertebrae as i n placentals and there are
u s u a l l y 7 lumbar vertebrae.
The pectoral g i r d l e i s s i m i l a r t o t h a t o f the
placentals, whereas the p e l v i c g i r d l e d i f f e r s
w i t h t h e presence o f the epipubic bones (may be
r e f e r r e d t o as the marsupial bones) and i s
s i m i l a r t o t h a t o f the monotremes. These
epipubic bones are two Large, f l a t bones, which
curve forwards and outwards from the m i d l i n e
and have the general form o f p a r t i a l crescents.
These bones are o n l y l i g h t l y joined t o other
bones, and take up the special stresses
produced by the abdominal muscles and pouch.
The hands u s u a l l y c a r r y f i v e d i g i t s and armed
with claws, but t h e nunber o f toes i s o f t e n
reduced and may bear h o o f - l i k e structures.
The marsupial egg has a very unequal cleavage,
there i s v i r t u a l l y no placental development and
instead u t e r i n e m i l k may be taken up by the
y o l k sac. The embryo may be born as young as 8
days from conception (e.g.the opossuns).
At b i r t h the young embryo w i l l leave the
vaginal opening and crawl t o t h e pouch and
become attached t o the teat.
I n order t o make t h i s journey t h e embryo
( c a l l e d a neonate) has well-developed forelimbs
and nervous system. I t mouth and o l f a c t o r y
system are w e l l developed and i s h i g h l y
specialized f o r suckling.
I n the pouch the neonate attaches t o t h e teat,
and t h e sides o f the Lips grow around the teat,
making i t almost impossible t o remove. M i l k i s
then i n j e c t e d i n t o the neonate. The Length o f
time i n the pouch i s v a r i a b l e between marsupial
forms. A wallaby may remain some 8 t o 9 months
i n i t s mother's pouch.
Marsupials also have delayed implantation.
Copulation can take place w i t h i n a day o f
b i r t h , but any 80 c e l l b l a s t o c y t e can remain
dormant f o r up t o 11 months. suspension o f
development i s c o n t r o l l e d by suckling o f the
young i n the pouch. Suckling stimulates a
release o f oxytocin and there are high l e v e l s
o f p r o l a c t i n which i n h i b i t s f u r t h e r development
o f the corpus Luteun.
PLACENTAL MAMMALS
SUBCLASS THERIA
INFRACLASS EUTHERIA
EIGHTEEN ORDERS
-
INSECTIVORA
-
DERMOPTERA
MACROSCELIDA
SCANDENTIA CHIROPTERA
PHOLIDOTA
TUBULIDENTATA
EDENTATA
PRIMATES
-
-
ROOENTIA -
- -
LAGOMORPHA
CETACEA
-
-
-
CARNIVORA
PROBOSClDEA
HYRACOlDEA
SIRENlA
-
-
-
PERISSODACTYLA
ARTIODACTYLA SlRENIA
-
-
small, p r i m i t i v e
insect-eating
f l y i n g Lemurs
elephant shrews
t r e e shrews
bats
phol idota
aardvarks
edentata
Lemurs, t a r s i e r s ,
monkeys, a p s , hunans
gnawing animals except
r a b b i t s and hyraxes
rabbits
whales, dolphins and
porpoises
modern meat-eating
elephants
hyraxes
seacows, manatees and
dugongs
odd-toed ungulates
even-toed ungulates
seacows, manatees and
dugongs
genetic material from the father. When i t
becomes connected t o the mother's body, i t
r i s k s imnunological r e j e c t i o n .
Nevertheless, placental mamnals can remain i n
the uterus, even u n t i l they are capable o f f u l l
m o b i l i t y . Even a f t e r b i r t h they are provided
w i t h m i l k f o r a f u r t h e r period.
b
The most widespread and diverse modern marmlals
are the placentals, a group whose young
complete t h e i r embryonic development attached
t o a placenta i n s i d e the mother's uterus.
b
ORIGINS
b
<
E a r l i e s t forms found i n t h e cretaceous period
and were a l l small insect-eating forms. During
t h e Palaeocene both carnivore and primates
evolved, i n the Late Cretaceous/Palaeocene the
ungulates had evolved.
b
CHARACTERISTICS OF PLACENTAL MAMMALS
b
A
b
The placental breeding technique spares the
young the hazardous journey outside t h e i r
mothers body a t a very e a r l y age. The placenta
permits the mother t o supply t h e i r every need
during the long g e s t a t i o n period. Animals such
as a whale o r seals could not have evolved
through the marsupial Lines.
Order i n s e c t i v o r a includes are v a r i e t y o f
insect-eating forms. There moles which Live i n
underground tunnels, hedgehogs which are spiny
and r o l l i n t o a b a l l as a defence against
predation, the desmans which swim w i t h webbed
f e e t and have a long snout which act as a
snorkel and shrews which are small a c t i v e
predators on insects. I n Madagascar there i s a
group c a l l e d the tenrecs, which are extemely
diverse being aquatic and t e r r e s t r i a l and some
even resemble hedgehogs.
Order dermoptera (= skin-winged) evolved from
insectivores and are comnonly c a l l e d f l y i n g
lemurs. These animals do not have t r u e wings,
but a f u r r e d s k i n extending from behind the
ears outwards t o the d i g i t s , along the sides o f
the body t o the t a i l . These f l a p s o f s k i n only
allow them t o g l i d e r a t h e r than t o f l y .
Possess n e i t h e r marsupial bones nor a pouch.
The foetus develops d i r e c t l y and e n t i r e l y
w i t h i n the body o f t h e female. The embryo i s
connected i n d i r e c t l y t o the mother v i a a
placenta t o t h e w a l l o f a uterus.
b
A placenta permits t h e embryo ( c a l l e d a foetus)
t o remain i n contact w i t h i t r s mothers uterus
f o r a Long time. A placenta i s a f l a t d i s k
t h a t becomes attached t o the wall o f the uterus
and i s connected t o the foetus by an umbilical
cord.
Order Macroscelidia are a l s o c l o s e l y a l l i e d t o
the insectivores and are comnonly c a l l e d the
elephant shrews which are h i g h l y specialized
f o r running w i t h very Large hindlimbs. Their
eyes are b e t t e r developed than t h e poorly
sighted insectivores.
b
Order scandentia include animals c a l l e d t r e e
shrews (Tupaia).
They are an intermediate
group between the i n s e c t i v o r e s and the primates
(apes and monkeys).
b
Order chiroptera includes t h e o n l y t r u e f l y i n g
mamnals the bats. Although they have obvious
i n s e c t i v o r e origins, t h e i r e n t i r e bone
s t r u c t u r e i s modified f o r f l i g h t . The wings
are formed by the elongated f i n g e r bones over
which i s tretched a naked s k i n membrane. Bats
can be dived i n t o small carnivores forms and
Large f r u i t eating forms. The small
carnivorous bats hunt using echolocation. This
bats emit high frequency c l i c k i n g sounds, which
s t r i k e objects and the echo i s returned t o the
bats using i t s Large ears t o receive them.
b
Order pholidota are comnonly c a l l e d pangolins
o r scaly anteaters. They possess Large scales
which are modified h a i r s and s h i e l d the animal
form predators. They a l s o have no teeth, but
do have an exceptionally Long s t i c k y tongue
(anchored t o the p e l v i s ) which i s used t o eat
ants and termites.
b
Order tubulidentata are comnonly c a l l e d
aardvarks and specializes i n e a t i n g ants and
termites and only occur i n southern A f r i c a .
L i k e the pangolins they have Long s t i c k y
tongues, but they are not toothless and possess
f i v e upper and f o u r lower cheek t e e t h on each
side o f t h e i r jaws ( i n c i s o r and canines are
The j u n c t i o n o f t h e placenta with the u t e r i n e
w a l l i s h i g h l y convoluted so t h a t the surface
area between the placenta and maternal t i s s u e
I t i s here t h a t the interchange
i s v e r y great.
between t h e mother and foetus takes place.
Blood i t s e l f does not pass from the mother t o
i t s foetus, but oxygen from her Lungs and
n u t r i e n t s derived from her food are both
dissolved i n her blood, d i f f u s e across the
j u n c t i o n and so enters i n t o the blood o f the
foetus. The waste products produced by the
foetus are absorbed by the motherrs blood and
then excreted through her kidneys.
THE PLACENTAL CONDITION MAKES FOR
COMPLICATIONS, ONE OF THE MOST SIGNIFICANT
BEING BIOCHEMICAL.
The mamnalian sexual c y c l e involves the regular
production o f a new egg. This causes no
problem t o t h e marsupial since the neonate
emerges before the next egg i s due t o be
produced.
Since t h e p l a c e n t a l remains much Longer i n the
uterus, t h e placental foetus promotes the
s e c r e t i o n o f hormones which suppresses the
motherrs sexual c y c l e during pregnancy.
The f o e t u s r s tissues are not the same
g e n e t i c a l l y as t h e mother's since i t contains
absent).
the e a r l y Cenozoic.
Order edentata are a v a r i e d group t h a t are
confined t o t h e new world( North and South
America) and includes anteaters, s l o t h s and
armadilos. Anteaters are toothless and have
s i m i l a r adaptations t o pangolins and aardvarks
f o r e a t i n g ants and termites (convergent
evolution).
Sloths and armadillos lack
i n c i s s o r s and canines, but do have s i n p l e cheek
t e e t h t h a t Lacks enamel and grow continuously
from t h e i r roots. The armadillo has 100 such
teeth. The a r m a d i l l o has bony p l a t e s on i t s
back f o r p r o t e c t i o n against predators. Sloths
are slow moving f u r r e d animals t h a t Live up i n
t h e trees. The p r e h i s t o r i c gound s l o t h s reach
imnense sizes up t o 5 metres (Megatherim) as
d i d some armadillos (Glyptodon) whose bony
p l a t e s formed a carapace t h a t was about 1,6 m
i n length.
Order Carnivora are m a t e a t i n g placentals t h a t
have prominent canine teeth. These are Long,
curved, pointed, very strong and p a r t i c u l a r l y
e f f e c t i v e f o r stabbing. Most carnivores are
predominantly meat-eaters and a l s o have short,
but sharp i n c i s o r teeth f o r nipping. The
f o u r t h upper premolar and f i r s t Lower molar
teeth have become s p e c i a l i z e d i n t o shearing
blades c a l l e d carnassial teeth (these are
absent i n aquatic carnivores such as seals).
Cats, dogs, Lions Leopards, cheetahs, Hyaenas
mongooses, bears, pandas (secondarily adapted
t o a herbivorous d i e t ) , seals, walruses,
sealions and elephant seals are a l l members o f
Carnivora.
Order Proboscidea i s represented by two species
o f elephant. Elephants are characterized by an
imnense size, and a long trunk t h a t i s r e a l l y a
h i g h l y modified nose. The tusks are elongated
upper incisors. Elephants have no canines o r
premolars and t h e i r molars are used t o g r i n d up
herbaceous food and are replaced successively
from behind as they wear down. They are naked
skinned since they l i v e i n t r o p i c a l climates
and t h e i r Large ears a c t as r a d i a t o r s t o
d i s s i p a t e excess heat. Their e x t i n c t
r e l a t i v e s , t h e mamnoths, had f u r and had
colonized cold, northern l a t i t u d e s u n t i l they
were hunted t o e x t i n c t i o n by p r e h i s t o r i c man.
Order primates includes Lemus, monkeys, apes
and man. They are e s s e n t i a l l y t r o p i c a l i n
d i s t r i b u t i o n and evolved from ancient, arboral
i n s e c t i v o r e s sometime i n t h e l a t e Cretaceous
period. Their t r e e - d w e l l i n g existence demanded
dextrous 1imbs, hands and f i n g e r s ( i n c l u d i n g an
opposable thumb), close set eyes w i t h
overlapping f i e l d s o f v i s i o n f o r depth
perception, e x c e l l e n t eye-hand co-ordination
and extended parental care f o r t h e i r young.
They are characterized by considerable
development o f the brain, a process t h a t
eventually r e s u l t e d i n the e v o l u t i o n o f man.
The e a r l i e s t ape-man was Australopithecus
africanus, a small-brained formed, followed i n
sequence by t h e Larger brained Homo h a b i l i s
(who used t o o l s ) and Homo erectus (had use o f
t o o l s and f i r e ) .
From t h i s stock two forms o f
modern man Homo sapiens evolved, one c a l l e d
Neanderthal man s u r v i v e i n c o l d northern
climates during t h e i c e ages, the other form
survives today as Homo sapien sapiens.
Order rodentia, i s t h e most abundant o f
p l a c e n t a l mamnal forms and includes, rats,
mice, mole-rats, s q u i r r e l s ( i n c l u d i n g forms
t h a t can g l i d e Like t h e f l y i n g lemurs),
porcupines, p r a i r i e dogs. They are a l l
characterized by a long p a i r o f prominent upper
and Lower incisors. These teeth are kept sharp
through d i f f e r n t i a l wear o f t h e i r enamel and
are v e r y e f f e c t i v e f o r gnawing. Canine teeth
are absent.
Order Hyracoidea includes t h e hyrax o r dassie,
which although s u p e r f i c i a l l y resemble rodents
and lagomorphs, are a c t u a l l y more c l o s e l y
r e l a t e d t o elephants. They are herbivores with
continuously growing chisel-shaped incisors.
They f e e t are completely d i s t i n c t i v e , there
being f o u r toes on the f r o n t feet, three on
the hind, terminating i n small, h o o f l i k e n a i l s .
Order Perissodactyla are odd-toed, hoofed
animals (=ungulates) and includes, horses,
asses, zebras, t a p i r s ( a l l having a s i n g l e
d i g i t ) and rhinoceoses (having three d i g i t s ) .
They are a l l Large herbivorous animals, and
many have elongated Limbs f o r f a s t e r running
speeds (horses and zebras). Their cheek teeth
are massive, strong and modified f o r g r i n d i n g
p l a n t material.
b
Order A r t i o d a c t y l a are t h e even-toed hoofed
animals and include antelope, deer, hippos,
g i r a f f e s , camels, Llamas, c a t t l e , sheep, pigs
and goats. These are generally herbivorous,
and with t h e exceptions o f p i g s and hippos are
ruminant animals (having a Large fore-stomach
c a l l e d a runen i n which p l a n t f i b r e s are
i n i t i a l l y digested). Many are grazing animals
and occur i n enormous herds and a l s o have
elongated Legs f o r f a s t e r running and t o avoid
predation. Their cheek teeth are large,
corrplex and designed f o r g r i n d i n g p l a n t
material (upper canine and i n c i s o r s are reduced
o r absent.
b
Order S i r e n i a are t h e aquatic dugongs and
mantees (sometimes c a l l e d sea cows).
They are
Large, h a i r l e s s herbivores (possessing o n l y
functional cheek teeth) t h a t have t h e i r
f o r e l i n ~ b smodified i n t o paddles and no h i n d
limbs. Possible share a s i m i l a r ancestry w i t h
elephants.
Order Lagomorpha includes r a b b i t s and hares and
a l l a r e s t r i c t l y ground dwelling forms.
Despite t h e i r s i m i l a r i t i e s t o rodents they are
not c l o s e l y related. L i k e rodents they do have
continuously growing i n c i s s o r s with a t o t a l o f
f o u r i n the upper jaw (two o f which are
reduced) as opposed t o only two i n the rodents.
Order Cetacea includes t h e most aquatic forms
o f mamnals; t h e whales, dolphins and porpoises.
The blue-whale i s t h e heaviest animal ever t o
have l i v e on t h e earth. Their modifications
f o r an aquatic existence include Loss o f the
hind-limbs, forelimbs have developed i n t o
f l i p p e r s , t h e t a i l i s f l a t t e n e d and most have a
dorsal f i n , t h e nasal opening (blow hole) i s on
t h e t o p o f t h e head, no external ears, h a i r i s
almost absent and i n s u l a t i o n i s by way o f
blubber. They can be d i v i d e d i n t o toothed
forms which are a c t i v e predators, and toothless
forms which have Long p l a t e s o f s t i f f h a i r - l i k e
material t h a t forms a baleen which acts as a
sieve t o f i l t r e plankton. Cetaceans are
i n t e l l i g e n t , s o c i a l animals, that can
comnunicate w i t h each other and use
echolocation t o navigate the waters they swim
i n . They probably evolved from insectivores i n