PORIFERA/CNIDARIA LABORATORY Phylum Porifera Class

PORIFERA/CNIDARIA LABORATORY
Phylum Porifera
Class Calcarea (Calciospongiae)
1. Leucosolenia, asconoid body type
2. Scypha, also referred to as Grantia, syconoid body type
a) Cross and longitudinal sections with spicules, eggs and different cell types
Class Hexactinellida (Hyalospongiae)
1. Euplectella sp. – Venus’ flower basket
Class Demospongiae
1. Demonstration specimens of various marine sponges (all leukonoid body type)
2. Commercial sponge spongin fibers
3. Sponge gemmules
Experiments (done per table)
1. skeletal composition and taxonomy
Phylum Cnidaria
Class Hydrozoa
Order Trachylina – no representatives
Order Hydroidea
Suborder Lymnomedusae
1. Hydra
a) live, note feeding reaction (use brine shrimp), note nematocyst
discharge
b) longitudinal and cross-section slides, observe cell organization/tissues
Suborder Leptomedusae (Calyptoblastea) – no representatives
Suborder Anthomedusae (Gymnoblastea) – no representatives
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 – no representatives
Order Semacostomeae
1. Aurelia aurita
a) whole specimen to observe rhopalia (sense organs)
b) scyphistoma stage
c) ephyra stage
Order Rhizostomeae
1. Cassiopeia
live specimens to observe movement
Class Anthozoa
Subclass Octocorallina (Alcyonaria) – no representatives
Subclass Zoantharia (Hexacorallia)
Order Zoanthidea – no representatives
Order Actinaria – the anemones
1. Metridinum
a) whole preserved specimens for dissection
b) cross-section and longitudinal slides
Order Madreporaria – true or stony coral
representatives
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
PHYLUM PORIFERA
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) and this class will not be covered in this lab.
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 or mesoglea. The mesoglea is not considered
to be a tissue since it contains a number of different kinds of independently functioning cells. Each cell
type in the mesoglea has a specific name, but the general term for all of these wandering cells is
amoebocyte.
3. Some of the amoebocytes in the mesoglea are specialized for secreting a skeleton. The sponge
skeleton may be composed of mineral spicules, spongin fibers or a combination of these two,
depending on the kind of sponge. Spicules may be calcareous (composed of Ca CO3) or siliceous
(composed of H2Si2O7). Spongin fibers are composed of a sulfur-containing schleroprotein.
4. 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.
5. 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
Morphologically, the bodies of sponges exhibit three distinct types based on the organization of their
internal canal systems. These three morphological types are designated as the ascon, sycon, and leucon
types. It is important to recognize that these three body forms represent morphological types and are
not directly related to the three classes of sponges. In fact, only a few species of sponges exhibit the
ascon and sycon body types. The majority of sponges are of the leucon variety.
I. ASCONOID - 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. 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.
II. SYCONOID - 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 (slides only)
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.
III. LEUCONOID - 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 Chondrilla nuculla 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. Each lab
table will receive a sample of “mystery sponge” in order to determine their taxonomy 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.
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 free-swimming 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
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 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.
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, 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
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 and mouths are called gastrozooids
and their function is feeding. The polyps without tentacles are called gonozooids and their function is
reproduction. Can you identify medusa buds 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 so that food ingested
by the feeding polyps can be circulated to nourish the non-feeding polyps. Observe the transparent
skeleton covering the polyps of the colony. This covering is secreted by the epidermis and is composed
of a polysaccharide called chitin.
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 gstrovascular cavities of all members of the colony are connected. Examine the preserved Physalia
available in the laboratory.
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.
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.
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.
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.
We will dissect and examine the anemone Metridium as a representative anthozoan. Examine a
cross section of your Metridium and locate the following: pharynx, siphonoglyph, complete and
incomplete septa, gastrovascular cavity, retractor muscles, gastrodermis, mesoglea, and epidermis.
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.
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. Examine the locomotion of a live specimen of
Mnemiopsis (if available) under a dissecting scope in a large fingerbowl.
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.