Download Porifera and Cnidaria

BIO170 General Biology Freeman/Mac Leod FMCC
PORIFERA AND CNIDARIA
Objective: After completing this exercise, you should be able to do the following:
 Compare the anatomy of the representative animals describing similarities and
differences in organs and body form that allow the animal to carry out body functions.
 Discuss the relationship between body form and the lifestyle or niche of the organism.
 Describe features of the phyla: Porifera and Cnidaria.
Introduction
Animals are classified in the domain Eukarya within the unikonta (1 flagellum) lineage. They
are the only multicellular organisms that are heterotrophic via ingestion. Careful study of
comparative anatomy, embryology, and most recently genetic and molecular data, reveals many
similarities in structure and development. Collectively, this evidence implies an ancestral
evolutionary relationship among all animals. Scientists recognize over 30 phyla of present-day
animals based on differences in body architecture.
A. STUDYING ANIMAL FORM AND FUNCTION
In this and the following lab exercises, you will investigate body form and function in examples
of several major groups of animals. You will use these investigations to ask and answer
questions comparing general features of morphology and relating these features to the lifestyle of
each animal observed.
The animals you will study in the next few lab exercises are sponge, hydra, planarian,
earthworm, clam, crayfish, grasshopper, sea star and pig. As you study each animal, relate your
observations to the unifying themes of this course: phylogenetic relationships, criteria that are the
basis for animal classification, the relationship between form and function, and the relationship
of the environment and lifestyle to form and function. Some of this will become more apparent
as we work through chapters 41-48 in your lecture textbook.
In your comparative study of these organisms, you will investigate 13 characteristics. Before you
begin the dissections, become familiar with the following characteristics and their descriptions:
1. Symmetry. Is the animal radially symmetrical (part arranged around a central axis),
bilaterally symmetrical (right and left halves are mirror images), or asymmetrical (no
apparent symmetry)?
2. Tissue organization. Are cells organized into well-defined tissue layers (structural and
functional units)? How many distinctive layers are present? Remember that
embryologically these tissue layers are ectoderm, mesoderm and endoderm.
3. Body cavity. Is a body cavity present? A body cavity – the space between the gut and the
body wall – is present only in three-layered organisms, that is, in organisms with the
embryonic germ layers ectoderm, mesoderm and endoderm. There are three types of
body forms related to the presence of the body cavity and its type (figure 2):
1
BIO170 General Biology Freeman/Mac Leod FMCC
a. Acoelomate - without a body cavity. Tissue from the mesoderm fills the space
where a cavity might be; therefore, the tissue layers are closely packed together.
b. Pseudocoelomate - a cavity between the endoderm and the mesoderm.
c. Coelomate - cavity within the mesoderm (completely surrounded by mesoderm).
Figure 1: The three types of body plans
4. Openings into the digestive tract. Can you detect where food enters the body and
digestive waste exits the body? Some animals have only one opening, which serves as
both a mouth and an anus. Others have a body organized as a “tube within a tube,” with
an anterior mouth and a posterior anus.
5. Circulatory system. Does this animal have open circulation (the blood flows through
coelomic spaces in the tissue as well as in blood vessels), or does it have closed
circulation (the blood flows entirely through vessels)?
6. Habitat. Is the animal terrestrial (lives on land) or aquatic (lives in water)? Aquatic
animals may live in marine (sea) or fresh water. Note how the organism is adapted to its
habitat.
2
BIO170 General Biology Freeman/Mac Leod FMCC
7. Organs for respiration (gas exchange). Can you detect the surface where oxygen enters
the body and carbon dioxide leaves the body? Many animals use their skin for
respiration. Others have special organs, including gills in aquatic organisms and lungs in
terrestrial organisms.
8. Organs for excretion. How does the animal rid its body of nitrogenous waste? In many
animals, these wastes pass out of the body through the skin by diffusion. In others, there
are specialized structures. You will learn about these structures as we investigate each
organism.
9. Type of locomotion. Does the organism swim, crawl on its belly, walk on legs, burrow
in the substrate, or fly? Does it use cellular structures, such as cilia, to glide its body over
substrate?
10. Support system. Is there a skeleton present? Is it an endoskeleton (inside the epidermis
or skin of the animal) or is it an exoskeleton (outside the body wall)? Animals with no
true skeleton can be supported by water: fluid within and between cells and in body
chambers such as a gastrovascular cavity. A coelom may provide a hydrostatic
skeleton.
11. Segmentation. Can you observe linear repetition of similar body parts? The repetition of
similar units, or segments, is called segmentation. Can you observe any degree of
segmentation? Have various segments become modified for different functions?
12. Appendages. Are there appendages (organs or parts attached to a trunk or outer body
wall)? Are these appendages all along the length of the body, or are they restricted to one
area? Are they all similar, or are they modified for different functions?
13. Type of nervous system. Do you see a brain and nerve cord? Is there more than one
nerve cord? What is the location of the nerve cord(s) (dorsal or ventral)? Are sensory
organs or structures present? Where and how many? Do you see signs of cephalization
(the concentration of sensory equipment at the anterior end)? What purpose do such
structures serve (for example eyes for light detection)?
As you carefully study or dissect each organism, refer to these 13 characteristics, observe the
animal and record your observations in the summary table provided to you. Tape or paste
that table into your notebook.
3
BIO170 General Biology Freeman/Mac Leod FMCC
B. PHYLUM PORIFERA – THE SPONGES
Introduction
Within the animal kingdom, sponges are separated from all other animals because of their unique
body form. This phylum consists of approximately 7000 species all of which are benthic; they
live attached to the bottom of aquatic environments. Sponges are characterized by the
possession of a feeding system unique among animals. Poriferans don't have mouths; instead,
they have tiny pores (ostia) in their outer walls through which water is drawn (figure 2). Water
enters through the ostia, flows through canals to a spacious chamber called a spongocoel, and
finally exits through large openings called oscula. Sponge cells perform a variety of bodily
functions and appear to be more independent of each other than are the cells of other animals.
Sponges come in an incredible variety of colors and an amazing array of shapes. They are mostly
marine living animals found at all latitudes beneath the world's oceans. Generally, they are
sessile, though it has been shown that some are able to move slowly (up to 4 mm per day) within
aquaria. Some sponges reproduce asexually but the primary method of reproduction is sexual
(Figure 3.) Sperm, released by the male, travel to the female where they are taken up by
choanocytes. The choanocytes deliver the sperm to amoebocytes that move through the
mesohyl. The amoebocytes deliver the sperm to the egg for fertilization. The zygote develops
in to a motile larva that is released to find a place to settle and develop into a new sponge.
You will observe the unique sponge structure by observing first a preserved specimen and then a
prepared slide of a section taken through the longitudinal axis of the marine sponge Scypha. You
will be able to observe other more complex and diverse sponges on demonstration.
Procedure:
1. Refer to your photo atlas pg. 83-85 as you work through this exercise.
2. Obtain the preserved sponge Spongilla. Using a stereoscopic microscope observe its external
characteristics.
a. Note the vase-like shape of the sponge and the osculum, a large opening in the body
at one end. The end opposite the osculum is the holdfast that attaches the animal to
the substrate.
b. Note the invaginations in the body wall, which form numerous fold and channels.
Identify the ostia. You may be able to observe needle-like spicules around the
osculum and protruding from the surface of the body. These spicules are made from
calcium carbonate or silica. They give support and provide protection by preventing
small animals from entering the sponge’s internal cavity.
c. Draw and label the bold terms above in your notebook.
3. Obtain a prepared slide of Scypha, longitudinal and cross section. Use a compound
microscope.
a. Follow the path that water would take through the organism.
i. Find an ostium, incurrent canal, radial canal and the spongocoel.
4
BIO170 General Biology Freeman/Mac Leod FMCC
ii. Draw these in your notebook and indicate current flow by drawing an arrow
from outside the organism into the spongocoel.
b. Note the structure of the body wall. You should be able to observe 3 kinds of cells.
i. One cell type that is unique to sponges is the choanocyte (or collar cell). These
cells line the spongocoel and the channels leading to it. Each collar cell has a
flagellum extending from its surface. The collective beating of all flagella moves
water through the sponge body. Small food particles taken up and digested by
collar cells are one major source of nutrition for the sponges. How would you
hypothesize about the movement of oxygen and waste throughout the sponge body
and into and out of cells?
ii. Epidermal cells form a continuous protective layer over the outside of the
organism.
iii. The third type of cells is called amoebocytes. These cells digest and distribute
nutrients from the choanocytes to the epidermal cells. They also transport waste
and help with repair and reproduction. As their name suggests, they move like
amoebas through the mesohyl (a gelatinous matrix of protein that also houses the
spicules and a substance called spongin) of the sponge.
iv. Draw and label the bold terms above in your notebook.
4. Observe examples of more complex sponges on demonstration. The body of these sponges,
sometimes called “bath sponges”, contains a complex series of large and small canals and
chambers. The same cells that were describes in Scypha are present in bath sponges, but, in
addition to spicules, there is supportive material that consists of a soft proteinaceous
substance called spongin. These sponges often grow to fit the shape of the space where they
live, and observing them gives you a good clue about the symmetry of the sponge body.
a. How would you describe the symmetry of sponges?
5. Complete the summary table provided, filling in all information for sponge characteristics
in the appropriate row. Tape or paste this table into your notebook. You will be adding
data over the next few lab exercises.
5
BIO170 General Biology Freeman/Mac Leod FMCC
Figure 2: Anatomy of a sponge
Figure 3. Reproduction and Development in Poriferans
C. PHYLUM CNIDARIA - JELLYFISH, CORALS, SEA ANEMONES
Introduction
The name Cnidaria comes from the Greek word "cnidos," which means stinging nettle. Casually
touching many cnidarians will make it clear how they got their name when their cnidocytes
(stinging cells) eject barbed threads (nematocysts) tipped with poison (Figure 4.). Cnidarians are
united based on the presumption that their cnidocytes have been inherited from a single common
ancestor. This adaptation allowed them to become successful marine predators. Today there are
about 11,000 species in four lineages: the Hydrozoa (hydroids), Cubozoa (box jellyfish),
Scyphozoa (jellyfish), and Anthozoa (anemones, corals and sea pens).
6
BIO170 General Biology Freeman/Mac Leod FMCC
Typical cnidarians are radially symmetric diploblasts (Figure 5). The outer epidermis contains
the cnidocytes. The gastrodermis lines the gastrovascular cavity, which in some cnidarians
may be divided up by septa or elaborated into branching canals. In between epidermis and
gastrodermis is the mesoglea, a layer of jellylike substance which contains scattered cells and
collagen fibers. A ring of tentacles often, but not always, surrounds the mouth (which also
functions as an anus).
Cnidaria reproduce sexually (Figure 6). During their life cycle, they take on both a medusa
forma and a polyp form. The medusa produces gametes that are shed in the water. The
fertilized egg develops into a mobile planula larva which settles and develops into a polyp.
Medusae are produced asexually from the polyp and are released to be dispersed.
Figure 4. Cnidocyte with nematocyst
Figure 5. Anatomy of Cnidaria
7
BIO170 General Biology Freeman/Mac Leod FMCC
Figure 6. Cnidaria Life Cycle
Figure 7. Hydra nerve net
Procedure:
1. Refer to your photo atlas pg. 86-87 as you work through this exercise.
2. Place several drops of culture water in a depression slide. Use a pipette to obtain a living
hydra from the culture and place it in the drops of water. Using a stereoscopic microscope
observe the hydra structure
a. Note any movement, the symmetry and body structures present (see bold terms
above)
b. Draw and label the bold terms above in your notebook.
3. Add one or two water fleas (Daphnia) to the slide and note the hydra’s behavior.
a. Set the slide aside and return to it in a moment.
4. Obtain a prepared slide of Hydra.
a. Draw and label the bold terms above in your notebook.
5. Not visible with the microscope is a network of nerve cells in the body wall, which serves as
the nervous system; there is no concentration of nerve cells into any kind of brain or nerve
cord (Figure 7).
6. Observe the central cavity, called a gastrovascular cavity. Digestion begins in this waterfilled cavity (extracellular digestion), but many food particles are drawn into cells in the
gastrodermis lining the cavity where intracellular digestion occurs.
7. To better observe cnidocytes and nematocysts, turn your attention again to your living hydra
and follow this procedure:
a. Use your living Hydra preparation from the previous procedure carefully place a
coverslip onto this depression slide. Place the slide on the stage of a compound
microscope and observe your living hydra first using the scanning and then the low
8
BIO170 General Biology Freeman/Mac Leod FMCC
power objective. Make sure your light source is not heating up the slide too much and
cooking your Hydra!
b. You should be able to focus on the tentacles. The cnidocytes will appear as swellings.
c. Put on your goggles and add a small drop of methylene blue to the edge of the
coverslip. Locate several cnidocytes with nematocysts coiled inside.
d. Draw and label the bold terms above in your notebook.
8. Switch to the low power objective. Add a drop of 1% acetic acid to the edge of the coverslip
and watch the rapid discharge of nematocysts from the cnidocytes.
a. Using the high power objective study the discharged nematocysts.
b. Draw and label the bold terms above in your notebook.
9. Complete the summary table provided, filling in all information for sponge characteristics
in the appropriate row. Tape or paste this table into your notebook. You will be adding
data over the next few lab exercises.
9