Class Calcarea (Calciospongiae)

PORIFERA LABORATORY
Phylum Porifera
Specimens and Slides:
Class Calcarea (Calciospongiae)
1. Leucosolenia, asconoid body type
a) live animals for structure and filtration
b) slides
2. Scypha, also referred to as Grantia, syconoid body type
a) whole preserved specimens
b) cross sections sowing spicules, eggs and different cell types
Class Hexactinellida (Hyalospongiae)
1. Euplectella sp. – Venus’ flower basket
Class Demospongiae
1. Demonstration specimens of various marine sponges
2. Commercial sponge sponging fibers
3. Sponge gemmules
Experiments:
1. pathway of filtration (Leucosolenia)
2. skeletal composition and taxonomy
1
A. TAXONOMY
Class Calcarea - sponges having calcareous spicules with 1 to 4 rays (asconoid, syconoid, leuconoid).
Class Hexactinellida - sponges having siliceous spicules with 6 rays. These spicules are often fused to
form a beautiful lattice-like cylinder, as in the so-called Venus' flower basket Euplectella (syconoid).
Class Demospongiae - contains sponges having siliceous spicules (not 6-rayed) and/or spongin fibers
(leuconoid).
Class Sclerospongiae - sponges having an internal skeleton of siliceous spicules and spongin fibers plus
an outer encasement of calcium carbonate. Only six species from the Caribbean have been described to
date (leuconoid). No representative specimens available in class.
B. PRINCIPAL FEATURES
The sponges are the first metazoans (multicellular animals) that we will study. The principal features of
phylum Porifera are listed below.
1. While some sponges are radially symmetrical, the majority of sponges are asymmetrical in body form.
Sponges are considered to be at a cellular grade of construction; that is, they have cellular differentiation
(tissues) without cellular coordination.
2. The outermost tissue layer of sponges is composed of cells called pinacocytes. In some sponges this
outer tissue layer is syncytial while in others the pinacocytes are all distinctly separated from one another
by cell membranes. The innermost tissue layer is composed of cells called choanocytes or collar cells
with flagella that beat to produce water currents through the sponge body. Between these two tissue layers
is a gelatinous layer called the mesohyl. The mesohyl is not considered to be a tissue since it contains a
number of different kinds of independently functioning cells. Each cell type in the mesohyl has a specific
name, but the general term for all of these wandering cells is amoebocyte.
3. Some of the amoebocytes in the mesohyl are specialized for secreting the skeletal elements and are
referrred to as sclerocytes. The sponge skeleton may be composed of mineral spicules, spongin fibers or a
2
combination of these two, depending on the sponge class. Spicules may be calcareous (composed of Ca
CO3) or siliceous (composed of H2Si2O7). Spongin fibers are composed of a sulfur-containing
schleroprotein.
4. The amoebocytes that are surrounding the pores and sometimes canals are considred to be porocytes
and are contractile cells that aid in water flow within the sponge body.
5. Water enters the body of a sponge by way of a number of minute incurrent pores or ostia. Water
leaves the body by way of one or more large excurrent pores or oscula. Within the body of the sponge,
the water may pass through a large cavity (the spongocoel) through a system of canals and chambers, or
through a combination of these two.
6. Movement of water through the sponge body is accomplished by the beating of the choanocyte flagella.
The choanocyte cells line either a spongocoel or a number of small chambers, depending on the sponge. A
choanocyte cell consists of a nucleus, one or more vacuoles, a long flagellum and a delicate, collarlike
structure which surrounds the base of the flagellum. Electron microscope studies show the collar of a
choanocyte to be composed of a circular arrangement of microvilli-like structures extending outward from
the cell body. The rotary motion of the flagellum forces solid food particles in the incoming water to
adhere to the outside surface of the collar. The streaming protoplasm of the collar transfers the food to the
collar base where ingestion can occur.
C. BODY TYPES
I. ASCONOID
Asconoid Type - Water entering the sponge passes through ostia that are actually openings within
doughnut-shaped cells called porocytes, which are found only in asconoid sponges. The water enters the
large central cavity called the spongocoel, which is lined with choanocytes. Water exits from the
spongocoel
Example Leucosolenia
Asconoid sponges are the simplest and most primitive sponge architectural type and are all relatively
small due to their inefficient filtering system. Their structure is demonstrated in Leucosolenia.
1. Whole Leucosolenia. Obtain a small colony of Leucosolenia sponges and place it in a dish filled with
seawater. Examine it under a dissecting microscope.
a) Mobility = Does it respond to a stimulus? Do you detect movement?
3
b) Filtration = To observe the filtering mechanism of Leucosolenia, prepare a dilute suspension of
carmine powder and seawater and then gently place a drop of the suspension near the colony.
Describe the water movement through Leucosolenia. Where do the carmine particles enter? Where
do they exit? Do particles enter the sponge at the same velocity that they exit? Explain.
c) Budding = Do you see budding on your Leucosolenia colony? If so, where are the buds
positioned? Examine the colonial structure of Leucosolenia. Describe how you think the ultimate
colonial form develops from a single sponge tube.
2. Cut Leucosolenia. From your Leucosolenia colony remove a single sponge tube for closer examination
and then rinse the colony in fresh seawater and return it to the holding tank. Cut the sponge tube
longitudinally into two halves (from osculum to base) and place the two halves on a slide so that half the
tube shows the inner surface and the other half shows the outer surface. Add a drop of saltwater and cover
with a coverslip. Examine both surfaces under the compound microscope (start at the lowest
magnification.
a) Cell types = Try to identify porocytes, pinacocytes, and choanocytes, or evidence of their
presence.
b) Skeletal elements = Tease apart the sections of sponge with a dissecting needle and examine for
spicules and amoebocytes. Describe the shape and arrangement of the spicules. How are spicules
formed? Do you see any evidence of this in your preparation?
Leucosolenia Slides. Examine the prepared slides. The outermost layer is the pinacoderm, which
contains the occasional porocytes. In a longitudinal section you will be able to see the cylindrical
spongocoel, lined with choanocytes identified by the presence of microvilli. You may also find
pinacocytes that form much of the epidermis of sponges and are as close as a sponge gets to having a
tissue. The skeletal elements, or spicules, are made of calcium carbonate and can be found in the
sclerocytes.
II. SYCONOID
Syconoid Type - Water enters the sponge through ostia, openings between cells, rather than within cells
as in asconoid sponges. Water then passes into radially arranged incurrent canals which lead to flagellated
chambers lined with choanocytes. Water leaves the flagellated chambers by way of excurrent canals that
lead to the spongocoel, which is lined a simple flat epithelium. Water exits from the spongocoel by way
of a single large osculum. Note that the body wall of syconoid sponges is thicker than that of asconoid
sponges and that the syconoid spongocoel is not lined by choanocytes as is the asconoid spongocoel.
Example Grantia or Scypha (same organism, two genus names with Scypha being the name found in
older textbooks)
Syconoid sponges are more complex than asconoid sponges. Syconoid sponges look like large asconoid
sponges, having a tubular shape, and each individual has a single excurrent osculum. The body wall is
thicker, however, and the spongocoel is lined with pinacocytes. The choanocytes line finger-like
chambers (radial canals), which permeate the spongocoel. Because this arrangement provides a more
efficient pumping system than the asconoid design, syconoid sponges are larger than asconoid sponges.
Obtain a single specimen of Scypha, a representative syconoid sponge. How does the colonial form of
Scypha compare to Leucosolenia? Section the Scypha and examine its body wall structure. Examine the
mesohyl and characterize the spicules of Scypha (p.52 of S&S). The prepared slides of a second syconoid
sponge, Grantia, clearly shows wall structure, pinacocytes, choanocytes, incurrent and radial canals, ostia,
apopyle(pore between radial canal and spongocoel), osculum, oocytes, spicules and gemmules (resistant
overwintering bodies containing archaeocytes and spicules. What are their structures and functions?).
4
III. LEUCONOID
Leuconoid Type - The ostia of a leuconoid sponge are like those of a syconoid sponge. These ostia lead
into a complex system of canals and flagellated chamgers that penetrate the very thick, dense mesoglea.
There is no spongocoel in a leuconoid sponge. Rather, water reaches the oscula by way of large excurrent
canals. The complex canal system of leuconoid allows for greater surface area over which water may pass
and consequently creates an increased area for food and oxygen uptake and for waste removal. It is not
surprising, therefore, that leuconoid sponges are the largest in size of all the types and that the vast
majority of sponges are leuconoid.
Leuconoid sponges are by far the most complex architectural-type of sponge. Most leuconoids are
colonial, and although individual oscula can be distinguished, it is difficult to separate individual
members of the colony. The vast majority of sponges are leuconoid. Examine the anatomy of the
leuconoid sponges available in the laboratory. How do you think its filtration system differ from the
asconoid and syconoid sponges you examined?
D. SPICULE COMPOSITION AND STRUCTURE
The systematics of sponges are based primarily on the composition and structure of spicules rather than
on architectural plan. Spicules are composed of either calcium carbonate or silicon dioxide, and the
skeleton may consist entirely of collagenous fibers (spongin) or a combination of spicules and spongin.
See the poriferan taxonomy for the characteristics of the four classes of Porifera. The class membership of
sponges is easily determined using the following tests:
1. The organic matrix of sponges (spongin) dissolves when boiled in 5% sodium hypochlorite solution.
Place small pieces of sponge tissue in 1-2 ml of the sodium hypochlorite solution in a testtube to carry out
this test. Boil the mixture for 2-3 minutes of minutes by placing the test tube in a beaker of boiling water.
After cooling, examine under the compound microscope. Are spicules present? This technique is also
used to remove spongin from spicules to examine spicule form.
2. The inorganic chemical nature of spicules is determined by drawing acetic acid or dilute hydrochloric
acid under the cover slip of a wet mount of spicules. Calcium carbonate spicules dissolve when treated in
this manner, while silicon dioxide spicules are not influenced by the treatment.
3. Examination of the shape of spicules found in a sponge are also important taxonomic characteristics.
5
6
CNIDARIA/ CTENOPHORA LABORATORY
Phylum Cnidaria
Class Hydrozoa
Order Trachylina – no representatives
Order Hydroidea
Suborder Lymnomedusae
1. Gonionemus
a) whole preserved specimens
b) balancing organ, prepared slide
2. Hydra
a) live, note feeding reaction (use brine shrimp), note nematocyst discharge
b) budding Hydra, prepared slide
c) male and female Hydra, cross section
d) nematocysts
e) blastula
f) longitudinal section
Suborder Leptomedusae (Calyptoblastea)
1. Obelia
a) whole mount slide of hydroid
b) whole mount slide of medusa
c) slide of polyps and gonangia
Suborder Anthomedusae (Gymnoblastea)
1. Pennaria
whole mount slide of hydroid with gonophores
2. Tubularia
whole mount slide of hydroid with gastrozoids
Suborder Chondrophora – no representatives
Order Siphonophora
1. Physalia
a) whole preserved colonies
b) cross section slide of tentacle, note nematocysts
Order Milliporina – no representatives
Class Scyphozoa
Order Stauromeduseae – ne representatives
Order Semacostomeae
1. Aurelia aurita
a) whole specimen for morphological analysis
7
b) scyphistoma stage
c) ephyra stage
d) strobila larva
e) planula larva
Order Rhizostomeae
1. Cassiopeia
live specimens to observe movement
Class Anthozoa
Subclass Octocorallina (Alcyonaria)
Order Gorgonacea (the gorgonans) - demonstration specimen
Order Pennatulacea (the sea pansies) – demonstration specimen
Subclass Zoantharia (Hexacorallia)
Order Zoanthidea – no representatives
Order Actinaria – the anemones
1. Metridinum
a) whole preserved specimens for dissection
b) cross-section slides
c) longitudinal section slides
Order Madreporaria – true or stony corals
Representative specimens
Order Ceriantharia – burrowing anemones
no representatives
Phylum Ctenophora
Class Tentaculata – ctenophores with tentacles
Order Cydippida
1. Pleurobranchia
Order Lobota – no representatives
Order Beroidea – no representatives
8
The phylum Cnidaria includes such animals as jellyfish, sea anemones, corals and hydroids. This group
was originally referred to as phylum Coelenterata, a name still seen in many textbooks. Modern
taxonomists, however, prefer the phylum name Cnidaria, and use "coelenterate" only as a common name.
Closely related to the phylum Cnidaria is the phylum Ctenophora containing organisms called "comb
jellies." Both cnidarians and ctenophores are considered to be at the "tissue grade" of body construction.
In other words, their body cells are organized into tissues and these tissues are functionally dependent on
one another, but (excluding a few minor exceptions) these tissues are not organized into organs.
PHYLUM CNIDARIA
Cnidarians are radially symmetrical organisms that have one of two basic body forms: the polyp
form or the medusa form. Polyps are cylindrical in shape and are generally oriented in the environment
with their oral (mouth) surface directed upward and their aboral surface (opposite the mouth) attached
to a substrate. Medusae are umbrella- or bell-shaped, are generally free-swimming, and are oriented in the
environment with the oral surface directed downward and the aboral surface directed upward.
The life cycle of cnidarians often includes an alteration of sexual and asexual generations, a
phenomenon that is referred to as metagenesis. When metagenesis occurs, the polyp is the asexual
generation and the medusa is the sexual generation. A generalized life cycle occurs as follows: Medusae
produce gametes which unite to form zygotes. Each zygote divides repeatedly and develops into a freeswimming larval form called a planula larva. The planula larvae eventually settle and develop into
polyps. Each polyp then asexually produces medusae to complete the life cycle. This generalized life
cycle is modified greatly in different groups so that either the polyp or the medusa stage may be reduced
or even completely absent from the life cycle. When the medusa stage is absent from the life cycle, the
polyp reproduces both asexually and sexually.
Colony formation is very common in the phylum Cnidaria, especially among polyps. When
colonies form, there is a tendency for individuals within the colony to become specialized structurally and
functionally. This structural and functional specialization within a colony is referred to as polymorphism.
You will be observing several examples of polymorphic cnidarian colonies in the laboratory.
One particularly distinguishing feature of the phylum Cnidaria is that all members of the phylum
produce structures called nematocysts. Nematocysts are produced within cells called cnidoblasts (or
cnidocytes) and are discharged under the influence of mechanical, chemical or nervous stimuli.
Nematocysts function in defense, prey capture, and temporary anchorage of the body to a substrate. After
a nematocyst is released, its cnidoblast cell dies. New cnidoblast cells and nematocysts are therefore
continually being produced.
Despite the difference in shape between polyps and medusae, the internal structure of these two
body forms is very similar. Each has a central coelenteron or gastrovascular cavity which functions
both in digestion and in circulation of nutrients around the body. This cavity has a single opening to the
outside--the mouth-- through which food enters the body and undigested material leaves. The body wall
consists of three layers: an outer epidermis of ectodermal origin, an inner gastrodermis of endodermal
origin, and a layer called mesoglea between the two. The mesoglea is gelatinous in consistency and, in
some cnidarians, may have cells located in it. It is probably secreted by both the epidermis and the
gastrodermis.
Most Cnidarians are carnivorous and use nematocysts to capture prey. The processes of feeding
and digestion are relatively uniform throughout the Cnidaria. Captured food is passed into the mouth by
the tentacles or by a tract of cilia. Digestion is partly extracellular and partly intracellular. Extracellular
digestion takes place in the GV cavity as enzymes are secreted by gastrodermal cells lining the cavity.
Finally, gastrodermal cells phagocytize the partially digested food particles and digestion is completed
intracellularly.
Both the epidermis and the gastrodermis absorb oxygen for respiration directly from the
environment or from the GV cavity. Oxygen then diffuses to any underlying cells. In the same manner
9
waste products, such as carbon dioxide and ammonia diffuse outward from cells to the body surface.
There are no specialized organs or body surfaces for gas exchange or the elimination of wastes.
The phylum Cnidaria is divided into three classes based on characteristics such as life cycle, the
morphology of the GV cavity, and the presence or absence of cells in the mesoglea. The three classes are
Hydrozoa, Scyphozoa and Anthozoa.
Class HYDROZOA
The life cycle of hydrozoans typically exhibits metagenesis, alternating between an asexual
colonial polyp stage and a sexual medusa stage. However, within the class there are species that tend to
reduce either the polyp or the medusa stage of the life cycle. The hydrozoan medusa usually has a circular
shelf of tissue attached to the underside of the umbrella. This structure is called the velum and it functions
in medusa locomotion. In both polyp and medusa forms within class Hydrozoa, the mesoglea is acellular
and the gastrovascular cavity is a simple sac. One last distinguishing characteristic of the class is that
gonads are always formed from epidermal tissue.
Genus Gonionemus
In the life cycle of Gonionemus the medusa stage is conspicuous while the polyp is very reduced.
Each Gonionemus medusa produces either eggs or sperm, and the union of gametes results in the
formation of a planula larva. The planula grows into a minute solitary polyp (about lmm in size) that
asexually buds off other polyps. Each individual polyp then buds off a free-swimming medusa to
complete the life cycle. In some hydrozoan species closely related to Gonionemus, the medusa stage is
totally absent from the life cycle. In these species the planula develops into a polyp-like larva called an
actinula. The actinula larva develops directly into a polyp.
Genus Hydra
Although they are classically studied as "typical" cnidarians, Hydra exhibit several very unique
features. First of all, Hydra are freshwater organisms. This characteristic sets them apart not just from
other hydrozoans but from cnidarians in general.
A second characteristic that distinguishes Hydra from other hydrozoans (and also from
scyphozoans) is that there is no trace of a medusa or even a medusoid bud in the Hydra life cycle.
Typically, Hydra polyps are reproduce by asexual budding throughout the spring and summer, and they
turn to sexual reproduction only in the fall. At that time, gonads develop directly on the polyp. When
Hydra eggs are fertilized, they receive a protective covering that makes them resistant to freezing and
desiccation. The eggs will develop into new polyps when environmental conditions improve the following
spring.
10
A third unusual feature of Hydra relative to other organisms in its class is that Hydra polyps are
solitary rather than being colonial. The polyps do not secrete any type of skeleton, and the individual
animals are capable of considerable locomotion. Observe a living specimen of Hydra.
The reason Hydra are the standard cnidarian for study in the laboratory is because they are
generally available and cooperative in demonstrating a number of phenomena common to cnidarian
polyps. We will use Hydra today to examine polyp functions.
Obtain a few specimens of Hydra that have been starved for 48 hours and transfer them to a watch
glass containing pond water. Allow the animals to attach and relax and then note how the body column
elongates and the tentacles extend. Although Hydra are usually sessile, they can glide on their base, float
by means of gas bubbles secreted in the region of the basal disc, and somersault to escape predators.
These movements, however, are hard to elicit in a laboratory situation. Using a probe, examine how
different parts of a Hydra's body respond to a stimulus. Are all parts equally quick to respond? What does
this tell you about the nervous system of Hydra?
With a pipet, transfer some Artemia larvae to the dish with the Hydra. Carefully observe the
reaction of Hydra to the prey. Describe the feeding response. Note the movements of the tentacles and the
reactions of the hypostome. What are the effects on the prey? How are the prey held? Remove a prey
item from the tentacles with fine forceps, make a wet mount, and examine under high power of the
compound microscope. Examine and describe the nematocyst types found. To examine undischarged
nematocysts, remove a tentacle from a hydra with a forceps, place it on a slide, cover with a coverslip,
11
and examine under the compound scope. How are the cnidoblasts distributed on the tentacle? To observe
the discharge of nematocysts, draw 5% acetic acid under the coverslip while observing cnidoblasts. Let us
now try to determine the mechanisms responsible for feeding behavior in Hydra. Place a Hydra individual
in a watchglass of water and attempt to discharge nematocysts by mechanically stimulating a tentacle with
a probe or strand of hair. Do nematocysts discharge? Do you observe a feeding response in the
individual? Now place isolated fresh Hydra in a watchglass and examine their reaction to introducing
clam juice and reduced glutathione into the watchglass without applying mechanical stimulation.
Reduced glutathione is a chemical
In addition, obsere the preserved slides (diagram) of Hydra to find the attachment structure, gastrodermis,
epidermis, mesoglea, tentacles, mouth on the raised hypostome, coelenteron, buds and reproductive rgans
(ovary and testes). Where are the nematocysts found? Examine the thickness of the mesoglea? What does
it tell you about the size of the mesoglea and its relationship to the organismal size?
Genus Obelia
The life cycle of this hydrozoan has a fairly even emphasis on the polyp and medusa stages. The
polyp stage of Obelia is colonial and provides a good example of polyp polymorphism. Examine a live
colony of Obelia under the dissecting scope. Two different structural and functional types of polyps can
be observed in the colony. The polyps with tentacles, a mouth and a hydranth enclosed in the hydrotheca
are called gastrozooids and their function is feeding.
The polyps without tentacles are called gonozooids containing medusa buds allocated around a
blastostyle, enclosed by the gonotheca and containing a distal aperture. Their function is reproduction.
Can you identify medusa buds and other features within the gonozooids? These will eventually give rise
to free-swimming medusae.
All of the polyps of an Obelia colony share a common gastrovascular cavity or coelenteron enclosed
in the gastrodermis so that food ingested by the feeding polyps can be circulated to nourish the nonfeeding polyps. Observe the transparent skeleton covering the branching of the colony, the coenosarc,
enclosed in the periderm. This structure is secreted by the epidermis (periderm) and is composed of a
polysaccharide called chitin.
12
Genus Pennaria
Unlike Obelia which does have a prevalent medusa stage, Pennaria is best known for the polyp
state, which is revealed, under microscope examination, to form extensive and beautiful colonies. The
multiply stained specimen illustrated below is a member of the Pennaria genus, and was captured in
brightfield illumination on the MIC-D digital microscope. Pennaria feature tentacles that occur in two
forms: filiform (string-like) and capitate (club-shaped tip). The filiform tentacles resemble those of
Obelia gastrozoids, and are long and tapering, with batteries of nematocysts distributed over the entire
surface. In contrast, capitate tentacles occur with their entire nematocyst array confined to a single knob
on the tentacle end. In Pennaria, medusa buds (even very large examples) lack tentacles, and the gonads
develop in the epidermis of the manubrium.
Genus Tubularia (Hydractinia)
A genus of hydroids that appear to be furry pink tufts or balls at the end of long strings, thus
causing them to be sometimes be called "pink-mouthed" or "pink-hearted" hydroids. These specimens are
especially prevalent in shallow waters along the Delmarva Penninsula. As the Pennaria they are best
known for their polyp stage, specifically the gastrozooids (usually interconnected through stolons and
therefore forming a colonial organism, never forming a branched colony with separate zooid types),
which gives rise to individual medusa buds (never contained in actual gonozooids).
Genus Physalia
Physalia, commonly called the Portuguese man-of-war, looks like a large medusa but is actually a
floating hydrozoan colony. The float, which contains gas and keeps the colony buoyant, is so highly
modified that it is questionable as to whether it is a polyp or a medusa. The float is the first member of the
colony to develop and it asexually buds off the other individuals of the colony. These other individuals
are modified polyps and they hang down from the lower surface of the float. Three different types of
polyps can be observed: gastrozooids, gonozooids and dactylozooids. Gastrozooids and gonozooids
function as described for other hydrozoan colonies. Dactylazooids each possess an enormous,
nematocyst-bearing fishing tentacle, and function in defense and in capture of food (although food items
must be passed to the gastrozooids for ingestion). As in other hydrozoan colonies, the gastrovascular
cavities of all members of the colony are connected. Examine the preserved Physalia available in the
13
laboratory and determine the detailed structure of the dactylozooid tentacles by finding the cnidocytes
containing the nematocysts and their coiled thread tubes. In addition, trigger hairs or cnidocils may be
visible.
Class SCYPHOZOA
This class includes the exclusively marine “true” jellyfish and their related polyps. The medusa
stage is usually large and conspicuous in the life cycle, while the polyps are small or even lacking. The
gastrovascular cavity in both the polyp and medusa forms is divided into 4 gastric pouches. Medusa lack a
velum and have oral arms (4 frilly extensions of tissue that hang down around the mouth). Both polyps
and medusae have a cellular mesoglea, and gonads on the medusae are gastrodermal.
14
As a representative scyphozoan we will examine Aurelia, a common jellyfish found along the
Atlantic coast of North America. The free-swimming medusae produce gametes which give rise to small
polyps called scyphistomae. After a period of growth, the scyphistoma divides transversely to become a
strobila that resembles a stack of discs. Each of the "discs" becomes an ephyra larva, detaches from the
strobila and swims freely in the plankton. The ephyra larva will eventually grow into an adult medusa.
Examine prepared slides of Aurelia planula, scyphistoma, strobila and ephyra .
As was true for the Hydrozoa, scyphozoan polyps (scyphistomae) may asexually produce other
polyps in addition to producing medusae. New scyphistomae may be produced asexually by budding or
by producing structures called podocysts. A podocyst is formed when the basal disc of the scyphistoma
fragments off the parent polyp and becomes surrounded by a resistant covering of chitin. The cyst will
remain dormant for a while, but will eventually give rise to a new polyp. Podocyst formation is seen in a
number of different jellyfish species. Podocysts are produced seasonally and are able to survive winter
conditions that would kill the polyps. Podocyst production may represent an adaptation to extreme
environmental fluctuations. The production of podocysts is thus analogous to the production of resistant
eggs by Hydra.
Although scyphozoan medusae resemble hydrozoan medusae in general features, they differ in
that they lack a velum, they have a complex gastrovascular cavity, and they have compound sense organs
called rhopalia around the edge of the umbrella. In addition, the angles of the mouth are elongated into
four oral arms which are grooved, often frilled, and always heavily ciliated. Examine a live specimen of
Aurelia. Identify the oral arms, gastric pouches, rhopalia, tentacles, and gonads.
Genus Aurelia - Probably the most widely recognized jellyfish, the moon jelly has a transparent,
saucer-shaped bell and is easily identified by the four pink horseshoe-shaped gonads visible through the
bell. It typically reaches 6-8 inches in diameter, but some are known to exceed 20 inches. Recent evidence
suggests that there are several similar-looking species of moon jellies within a group of species that were
once called the moon jelly, Aurelia aurita. The moon jelly is only slightly venomous. Contact can
produce symptoms from immediate prickly sensations to mild burning. Pain is usually restricted to
immediate area of contact.
15
You shoul be able to identify the interradial gonads surrounded by the gastric pouches, the oral arms,
tentacles, rhophalia, and the overal canal systhem (no need to determine between different canals).
Genus Cassiopeia - The Upside Down Jellyfish, also called the Cassiopeia Jellyfish, is so named
because its flattened bell (head) rests on the bottom. It extends its frilly tentacles up into the water column
where they capture planktonic food and absorb light that is used by photosynthetic algae that are housed
in its body.
Why do members of Cassiopeia swim with theis tentacles pointing upward? Can you identify the
structures displayed in the diagram above in the live organism? Which structures are hard to discern?
Class ANTHOZOA
This remaining class of Cnidaria contains the sea anemones and corals. Medusae are completely
absent from the life cycle of anthozoans. The polyp produces gametes directly. Fertilized eggs develop
into planula larvae and each planula gives rise to a new polyp. In addition to sexual reproduction, polyps
may also reproduce asexually by budding or by fragmentation. Anthozoan polyps may be solitary or
colonial, depending on the group. The internal structure of the anthozoan polyp is more complex than that
of hydrozoan and scyphozoan polyps. The gastrovascular cavity is characteristically divided by a number
of radially arranged septa or mesenteries. The mesoglea is always thick and contains cells and fibrous
supporting material. The gonads are gastrodermal and are borne on the septa. Most Anthozoa have a
bilateral or biradial symmetry superimposed on their basic radial symmetry
The Anthozoa are divided into two subclasses: 1) Zoantharia (Hexacorallia) - sea anemones and
hard corals; and 2) Alcyonaria (Octocorallia) - soft corals and horny corals.
Subclass ZOANTHARIA
The tentacles and septa are often in multiples of six but never eight. The tentacles are always simple and
the skeleton, if present, is an exoskeleton made of calcium carbonate.
Sea Anemones - Sea anemones are solitary polyps that usually live attached to a hard substrate.
Sexual reproduction in anemones occurs as described for Anthozoa in general. Asexual methods of
reproduction involve not only budding, but also fragmentation and fission. In fragmentation small bits of
the basal disc are cast off as the anemone slowly creeps along. Each bit grows into a small anemone.
Fission refers to the splitting of an individual longitudinally into a few large pieces which become a new
polyp.
16
We will dissect and examine the anemone Metridium as a representative anthozoan. Examine a
cross section of your Metridium and locate the following: oral disc with tentacles, pharynx, siphonoglyph,
complete and incomplete septa, gastrovascular cavity, retractor muscles, gastrodermis, mesoglea, and
epidermis. You should also be able to determine some of these structures in the cross and longitudinal
slides of Metridium provided.
Hard Corals - The fundamental anatomy of the septa and the gastrovascular cavity of hard corals
closely resembles that of sea anemones. The major differences involve the colonial growth pattern of most
corals and the secretion of a massive calcium carbonate exoskeleton. Examine a colony of living
Astrangia and identify the basic external features of the polyps.
In the most generalized coral skeleton type, the portion of the exoskeleton directly around the
polyp resembles a cup with a floor and walls. Soon after the planula larva settles and becomes a juvenile
polyp, it begins forming an exoskeleton by secreting the floor of the coral cup. Almost at once the
undersurface of the polyp develops radial folds which secrete radially arranged ridges called sclerosepta.
These skeletal sclerosepta alternate with the tissue septa within the gastrovascular cavity of the body. At
the same time a rim is formed and built up as a wall around the polyp. Study a piece of coral from which
the polyps have been removed.
You should also take note of the great variety of overall shapes that entire coral colonies may
acquire. Some corals produce lateral branches, while others are encrusting or leaf-like. Still others form
large compact mounds. The overall shape of the colony is determined by the pattern in which new polyps
are asexually budded.
Subclass ALCYONARIA
17
This subclass includes sea fans (gorgonians) and sea pens (Renilla). They are always colonial.
Each individual polyp of the colony has eight pinnate (feather-like) tentacles, eight complete septa and a
single siphonoglyph. The mesoglea of alcyonarians is relatively thick. Running through the mesoglea are
numerous gastrodermal tubes that connect the GV cavities of individual polyps in the colony.
The alcyonarian skeleton is an internal one or endoskeleton that is secreted by the mesoglea. It is
generally in the form of microscopic spicules of calcium carbonate. However, the horny corals -- sea whip
and sea fan -- have an endoskeleton of horny protein material in addition to spicules. This horny skeleton
is important in giving support to the colony. The skeleton of another alcyonarian, the organ pipe coral, is
particularly interesting. This skeleton is composed of fused spicules stained red with iron salts. The
spicules are secreted by the mesoglea, but they end up encasing the polyps of the colony. The skeleton is
built into a series of tubes (each of which contains one polyp) strengthened by connecting transverse
platforms.
In several groups of Alcyonaria there is polymorphism of individuals within a colony. This is
illustrated nicely by the sea pansy and the sea pen. The sea pansy consists of a large primary polyp with a
stem-like base that is anchored in the sand. The upper part of the primary polyp gives rise to two types of
secondary polyps. Autozooids are ordinary polyps which bear tentacles, feed and reproduce.
Siphonozooids lack tentacles, are small and wart-like in appearance, and occur in clusters. They do not
feed, but rather serve to create a water current through the colony. What is the function of this water
current?
PHYLUM CTENOPHORA
The Ctenophora are among the most beautiful of marine organisms. They are transparent, pelagic animals
with bilateral symmetry superimposed on a basic radial symmetry. They are never colonial and have no
sessile stage. Their most characteristic features are ctenes, which are plates of fused cilia arrangea like the
teeth of a comb (see p. 172 Barnes). There are eight vertical rows of ctenes arranged at intervals around
the body. The ctenes in each row beat in metachronal waves and propel the organism's mouth forward
through the water.
Like Cnidarians, all ctenophores are carnivorous and may use tentacles to capture food. Only one species
of ctenophore produces nematocysts. All other ctenophores have colloblast cells, which function in food
capture by sticking to prey items.
18