Download Kingdom Animalia

ENCOUNTERS
WITH
LIFE
Kingdom Animalia:
Porifera, Cnidaria,
and Ctenophora Phyla
OBJ ECTIVES
After completing this exercise, the student
should be able to:
• Compare the Phyla Porifera, Cnidaria, and Ctenophora as to level of
organization---eellular, tissue, organ, system.
• Describe the feeding and nutrient processing of a sponge and a hydra.
• Identify the anatomical structures of the sponge and the hydra.
• Define the terms in boldface (other than the anatomical structures).
• Identify the phyla and classes of each of the animals in the jars on display.
• List the basic types of cell'in the sponge, and explain the function of each.
• Compare and contrast the two body forms of the Cnidaria.
• Describe the alternation of asexual and sexual reproduction shown by
Obelia.
• List the characteristics of Phylum Ctenophora
The Animal Kingdom
The animal kingdom is composed of multicellular,
obviously motile, heterotrophic organisms that repro­
duce sexually by oogamy and produce multicellular
embryos. You may wish to refer to Exercise 12 and
review the outline of animal taxa to be studied in the
next several exercises.
Phylum Porifera
The phylum Porifera contains animals known as
sponges. Porifera means "bearing pores." Although
sponges are multicellular, the cell aggregates of this
phylum do not form true tissues. But the cells have
differentiated to result in a division of labor such as
reproduction, feeding, and water circulation.
Many of these animals have body shapes resem­
bling vases, as illustrated in Figure 22.1. The walls of
sponges have numerous tiny openings called ostia,
through which currents of water enter, carrying food
and oxygen to the central cavity of spongocoel. The
movement of water is produced by the beating of the
flagella of collar cells, or choanocytes, in the flagellated
chambers, or radial canals. The choanocytes capture
and digest food particles brought in by the water cur­
rents with the aid of collar-like structures surrounding
their flagella.
The water entering the ostia circulates through
the incurrent canal, prosopyles (openings between
the incurrent canals and radial canals), radial canal,
apopyles (openings between the radial canals and the
spongocoel), and spongocoel and exits through the
opening at the top of the animal These parts are shown
in Figure 22.2. This opening is called the osculum.
The body wall consists of three layers.
1. The Outer layer consists of flat epithelial cells,
among which are contractile cells called pinaco­
cytes, which regulate the sizes of the ostia.
2. The middle layer consists of gelatinous non-living
matrix containing living mesenchyme cells called
amoebocytes, which are capable of amoeboid
movement. Amoebocytes have many functions.
They collect food from the flagellated collar cells,
secrete the gelatinous matrix, collect wastes, pro­
duce spicules, and can differentiate into any of the
other cell types. The spicules, which are minute
crystal-like structures composed of calcium salts
or silicious material, form the supportive skeleton
of the sponge.
3. The inner layer is composed of the radial canals
with their choanocytes, as mentioned previously.
Sponges are unique in that they are believed to
have evolved from a completely different group of
flagellates than did other animals. For this reason,
they are considered to be an evolutionary dead-end.
~;;::::::YLE
OSCULUM
~
EPIDERMIS
APOPYLE--1
CHOANOCYTE LAYER
_ _ ,' '~OSTIUM
MESENCHYME
1......iG--OSTIUM
FLAGELLATED CHAMBER-­
INCURRENT CANAL
iil $~~'
_....._
INCURRENT CANAL
8o ~~,l;.~.~~~~SPICULES
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A.
SIMPLE SPONGE Grantia
B.
Grantia CANAL SYSTEM
Figure 22.1 Grantia (L.S.)
(
Figure 22.2 Grantia (XSj
1.
2.
3.
4.
5.
Reproduction in sponges occurs asexually by
budding, fragmentation, and in freshwater forms, by
formation of gemmules. A gemmule consists of a ball
of amoebocytes surrounded by a capsule consisting
of spicules and dead cells. Sexual reproduction in
sponges involves the fusion of eggs and sperm formed
from amoebocytes. The zygote develops into a free­
swimming ciliated larva.
Obtain a prepared slide of the cross section of
Grantia. Sketch what you see, labeling the central
cavity, or spongocoel, incurrent canal, radial canal,
and choanocytes, with reference to Figure 22.2. Also
note the small openings, or apopyles, leading from the
radial canals into the spongocoel.
Obtain another slide showing the spicules which
form the skeleton of the sponge. Make a sketch of
Grantia spicules below.
The classification of sponges is determined largely
by shape and chemical composition of the skeleton.
The phylum Porifera is subdivided into three classes:
1. Class Calcarea-Calcareous or chalky sponges.
Example: Grantia
2. Class Hexactinellida-Glass sponges, composed of
siliceous spicules. Example: Venus Flower Basket
Spongocoel
Ostium
Incurrent canal
Radial canal
Apopyle
3. Class Demospongiae-Commercial or bath
sponges. Skeleton includes proteinaceous spongin
fibers. Example: Spongia
Examine the specimens of sponges in the display jars,
noting the class to which each belongs.
Phylum Cnidaria (Coelenterates)
The animals of the phylum Cnidaria demonstrate the
tissue level of organization. Although the cell aggre­
gates function as tissues, no true organs are present.
The body of the animal is composed of two epithelial
layers: an outer epidermis and an inner gastrodermis,
which lines the gastrovascular cavity, or coelenteron.
Between these two layers is a gelatinous layer of
mesoglea. The epidermis is a well-developed layer
of closely-packed cells that function to protect the
organism and obtain food. The gastrodermis is also
well developed and serves in digestion and internal
transport. The mesoglea is poorly developed, varying
from a jellylike substance containing a few cells, which
coordinate the actions of the organism and the pro­
duction of gametes, to a true cellular layer in the most
advanced members of the group.
The most distinguishing characteristic of this
phylum is the possession of specialized cells called
cnidoblasts. These cells contain stinging structures
called nematocysts, which are used for defense and to
capture food. A nematocyst is a capsule containing a
long coiled thread that shoots out and either traps
and holds the prey or injects a toxic substance that
paralyzes the prey or predator.
Another characteristic of these animals is that
they are polymorphic, displaying different body forms
at different points in the life cycle of the organism.
There two basic body forms, the polyp and the
medusa, as illustrated in Figure 22.3. The medusa is
generally a more active swimming form whereas most
polyps are sessile, remaining attached to some sub­
strate. Both forms are found in the life cycle of many
coelenterates. Some coelenterate colonies are com­
posed of both forms of individuals. Both forms are
basically radially symmetrical.
The phylum Cnidaria is subdivided into three
classes: Class Hydrozoa, Class Scyphozoa, and Class
Anthozoa.
CLASS HYDROZOA
Many members of the class Hydrozoa develop into
sessile polyp colonies such as Obelia. Their life cycles
characteristically involve a regular alternation be­
tween asexual (polyp form) and sexual (medusa form)
reproduction, although the polyp form tends to be
dominant.
Hydra is an exceptional member of this class­
a mobile individual polyp rather than a sessile or
colonial form. Reproduction occurs asexually by
budding or sexually by the production of sperm and
eggs, and it produces only polyps. No medusae pro­
duced at any time.
Obtain a prepared slide of a Hydra. Referring to
Figure 22.4, note the following parts as you find them:
•
•
•
•
•
basal disc, for attachment
cylindrical body
circle of tentacles
elevated hypostome at the base of the tentacles
a mouth in the center of the hypostome
• buds
• spermaries (swellings just beneath the tentacles)
• ovaries (swellings in the lower portion of the
body)
• nematocysts
• gastrovascular cavity
•
•
•
•
epidermis
mesoglea
gastrodermis
flagellum
Using a concave depression slide, prepare a wet
mount of living Hydra. Do not cover with a coverslip.
For the best results, reduce the amount of light enter­
ing the slide. Do not jar the table or microscope, as
any disturbance will cause the Hydra to contract.
Feeding the Hydra is optional. After viewing the
living Hydra, return it to the container marked Fed
Hydra.
MOUTH
TENTACLE
!t~-----MESOGLEA----------,,.e;.~%m~~
'S!=l------EPIDERMIS --------.(:7'
1 " - - - - - GASTRODERMIS ------tr;w
COELENTERON
(GASTROVASCULAR CAVITY)
TENTACLE
MEDUSA
POLYP
Figure 22.3 Body Forms of Cnidaria
TENTACLE
---.+..:.r.t
MOUTH
GASTROVASCULAR CAVITY
FLAGELLUM
EPIDERMIS
MESOGLEA
GASTRODERMIS
BUD
BASAL DISC
Figure 22.4 Hydra (L.S.)
Obtain a prepared slide of the colonial Obelia
and find the parts labeled on Figure 22.5. This colony
forms from the repeated budding of a single individual.
The various buds take up either reproductive (gonan­
gium or reproductive polyp) or feeding (hydranth or
feeding polyp) duties that the entire colony performs.
The reproductive polyp, or gonangium, produces
medusae which in turn produce eggs or sperm. When
fertilized, or when egg and sperm unite, the zygote
goes through various stages of embryonic development
and gives rise to a ciliated larvae, the planula. The
planula attaches itself to the substratum and gives
rise to a new asexual hydroid colony.
Another example of a Hydrozoan is Gonionemus,
which has a dominant medusa stage. For years, Go­
nionemus was thought to lack the polyp stage because
it was so small (1 mm.) that no one had been able to
detect it. The polyp cannot only produce medusae by
budding, but can also bud to produce other polyps.
Upon the completion of its development, the medusa
form of Gonionemus resembles a typical jellyfish, but
unlike scyphozoan jellyfish, it has a muscular shelf­
like velum around the margin of the "bell" which aids
in swimming. Figure 22.6 illustrates a hydrozoan
medusa.
Physalia, Portuguese man-of-war, shows great
diversity in that it consists of floating colonies of
specialized individuals. Each colony has at least four
types of polyps:
1. the pneumatoph ore, or float, into which gas is
secreted to render the colony buoyant
2. feeding polyps
MEDUSA
REPRODUCTIVE POLYP _~r-\--\---7
OR GONANGIUM
ZYGOTE
PLANULA LARVA
BLASTULA
Figure 22.5 Obelia Hydroid Colony
\
TENTACLES
VELUM
VENTRAL MOUTH
RADIAL CANAL
---.::~
CIRCULAR CANAL
GONAD
~
•
Figure 22.6 Gonionemus Medusa
3. defensive or stinging polyps
4. reproductive polyps.
MOUTH
Some species also have sensitive or feeling
polyps. Examine the hydrozoan specimens
on display in jars to identify their polyps.
CLASS SCYPHOZOA
The members of the class Scyphozoa are
commonly called jellyfish. Most of them
have both body forms in their life cycles,
although the medusa is dominant and the
polyp form may be very small. Scyphozoan
medusae do not have a velum as the hydro­
zoan medusae do. Refer to Figure 22.7 as
you examine the jellyfish on display in jars.
ORAL ARMS (LOBES)
Figure 22.7 Structure of Jellyfish, Aurelia
CLASS ANTHOZOA
All members of this class have the polyp body plan.
There are no medusa forms. Many of them, such as
the corals and sea pansies, live in colonies, and others,
such as the sea anemone, live independently. Examine
the representatives of this class on display and com­
pare them with the illustrations in Figure 22.8.
ROSE CORAL
Phylum Ctenophora
Members of phylum Ctenophora are often known as
the comb jellies (comb bearers) and sea walnuts. They
comprise about 80 species of free-swimming marine
animals with translucent gelatinous bodies. Cteno­
phores show resemblance to jellyfishes and at one
time were classified with the coelenterates (see Figure
22.9). The unique characteristic is that they possess
eight rows of swimming "combs," or ctenes, which
are composed of fused cilia; unlike the cnidaria, they
lack nematocysts, except for one species.
Observe the ctenophores on display.
Acropora
ELKS HORN
SEA ANEMONE
MUSHROOM
CORAL
BRAIN CORAL
Figure 22.8 Representative Anthozoans
SENSE ORGAN
STOMACH
COMB PLATES
MOUTH
Figure 22.9 A Ctenophoran
Review Questions
1. Two kinds of cells showing division of labor in a sponge are
and
_
_
2. Sponges reproduce by (describe each):
a.
b.
_
_
3. Why are sponges considered unique in the evolution of animals?
_
4. Identify the following:
Gastrovascular cavity
_
Nematocyst
_
Planula
_
Velum
_
Polyp
_
Medusa
_
Amoebocyte
_
Spicule.
_
Choanocyte
_
5. The unique characteristic of the Ctenophores is
6. Members of the Phylum Porifera demonstrate a (multicellular, tissue, organ system) level of organization.
7. Members of the Phylum Cnidaria demonstrate a (multicellular, tissue, organ system) level of organization.
_
8. List the openings and structures a droplet of water would pass on its way through the sponge. Begin with the
ostia and end with the osculum.
_
9. What cells are responsible for producing the water current?
_
10. List the functions of the amoebocytes. (Don't forget their reproductive functions!)
_
11. Name the two epithe1iallayers found in members of the Phylum Cnidaria and their functions.
a.
_
b.
_
12. For what reason(s) are cnidoblasts important to the Hydra?
_
13. How are polyps and medusas similar?
_
How are they different?
_
14. Why is the Hydra an exceptional member of the class Hydrozoa?
15.
--I
MATCHING:
_
Match the class with the correct organism or characteristic (a, b, or c).
_ _ _ 1. Hydra
_ _ _ 2. Jellyfish
a. Class Anthozoa
b. Class Scyphozoa
c. Class Hydrozoa
3. Gonionemus
_ _ _ 4. Obelia
5. Sea anemone
6. Coral
_ _ _ 7. Both polyp and medusa forms with polyp form being dominant
8. Medusa form is dominant, polyp form greatly reduced
_ _ _ 9. No medusa form, all polyps