Biol 124
Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
8-1
Biology 124 – Laboratory 8
Selected Invertebrate Phyla in Kingdom Animalia (I):
Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
Text Reference: Campbell Biology Cdn. Ed. (2014) p. 716 – 732
Illustration Reference: Campbell Biology Cdn. Ed. (2014) p. 721, 722, 725, 730; Biodidac
Introduction:
In total, there are about 35 animal phyla, with some sources recognizing fewer or more.
Only a handful of the more common phyla will be covered in the next three laboratories.
The saltwater tank in the lab usually has a number of representatives of these phyla – ask
your instructor to help you identify some of the marine species and sort them to phylum.
While vertebrate animals like mammals or birds may be the first to come to mind in
association with the term “animal,” all but one sub-phylum in one phylum of Kingdom
Animalia are actually comprised of invertebrate animals. Invertebrate animal species
account for roughly 95% of all animal species.
Station 1: Phylum Porifera – Sponge Body Plan
Sponges are most likely among the first animals to have evolved on this planet. They are
suspension feeders; sea water is circulated into the spongocoel (interior cavity of the
sponge), is filtered for fine suspended matter by individual collar cells (choanocytes), and
exits through a chimney-like opening, the osculum. In turn, sponges are not preyed upon
by many animals, but some sea turtles have an almost exclusive sponge diet.
Examine the external features of the sponges on display, and label the osculum,
epidermis, collar cells and pores in Fig.1 below.
Figure 1. Sponge Anatomy (© Campbell, 2014, p.721)
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Observe the sponges on display. As a group, they exhibit no pattern of symmetry (neither
radial nor bilateral), and are therefore called asymmetrical. However, 3 different body
plans are recognized in Porifera, based on their level of complexity: asconoid (e.g.
Leucoselenia) and syconoid (e.g. Grantia = Scypha) represented on slides, as well as
leuconoid (macroscopic specimens on display). Add sketches of these 3 different body
plans:
Station 2: Phylum Porifera – Sponge Skeleton
To aid in structural support, sponges possess internal skeletal elements called spicules,
made of calcium carbonate (“chalky” material), silica (“glassy” material) or of the flexible
protein spongin. Observe spongin and spicules under the compound microscope, and
make your own wet mount of a few glass sponge spicules - sketch a few of the different
shapes:
Which type of spicule would you expect in bath sponges? ______________________
Actually, most bath “sponges” in use these days are manufactured synthetically or from
different biological sources such as the fruit of Luffa vines in the cucumber family.
Station 3: Phylum Cnidaria – Cnidocytes
The phylum Cnidaria is named after a collective trait shared by all of its members to a
greater or lesser degree: cnidocytes (stinging cells), which are used in defense and prey
capture. A paralyzed or poisoned prey organism can more easily be manoevered by
tentacles into the gastro-vascular cavity. Cnidocytes are amongst the most complex cells in
the animal kingdom, with different combinations of venoms and barbs, e.g. the spear-like,
encapsuled nematocysts. Look at a slide with discharged nematocysts and make a
labeled sketch:
Station 4: Phylum Cnidaria – Body Plan
Cnidarians have radial symmetry, which means you can differentiate top and bottom of the
animal, but neither front/back nor left/right. Cnidarians lack a complete digestive tract with 2
openings; instead, their sac-like digestive tract has only 1 opening (mouth=anus!), and is
called a gastro-vascular cavity. There are two basic body plans, polyp and medusa based generally on whether the tentacles are facing up (polyp) or down (medusa). Label
the features discussed above in Fig. 2 below:
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Figure 2. Polyp and Medusa (© Campbell, 2014, p.722)
Examine a slide of the sea anemone Metridium under the compound microscope and
identify tentacles, mouth/anus and gastro-vascular cavity.
Look at the cnidarian diversity on display and complete the table below. Some cnidarians
exhibit only the polyp or only the medusa form, while others go through both body forms
during their life cycle.
Cnidarian
Hydroids
Jellies
(e.g. Hydra, Obelia)
Sea
Anemones
Corals
Dominant Body Form
(Polyp or Medusa)
Some cnidarians, like the Portuguese Man-of-war or Obelia form colonies with division of
labor. Examine a slide of the hydroid Obelia under the compound microscope, and
differentiate between feeding polyps and reproductive polyps. Add a labeled sketch:
Station 5: Phylum Platyhelminthes – Free-living Flatworms
Members of this phylum are dorso-ventrally flattened (top-bottom, as a pancake). This
flat shape provides sufficient surface area for diffusion of gases and metabolic wastes
through the body surface. Flatworms lack respiratory, circulatory and excretory systems.
Flatworms range in size from microscopic to over 30 m long. There are both free-living
flatworms (e.g. planarian worms) and parasites (e.g. tapeworms).
Look at the preserved freshwater planarian Planaria a.k.a. Dugesia under the dissecting
microscope. A live planarian may be available, and depending on its appetite, you may
have an opportunity to watch it feed. You should be able to identify the eyespots, the
pharynx, mouth/anus and a highly-branched gastro-vascular cavity. Label these
features in Fig. 3 below. Use labeled arrows to indicate where food is ingested, digested,
and egested from the body. What symmetry do flatworms have? _________________
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Figure 3. Planarian Anatomy (© Campbell, 2014, p.725)
Station 6: Phylum Platyhelminthes – Parasitic Tapeworms
Tapeworms are internal parasites of vertebrates. Different species of tapeworms infect
different species of hosts, from fishes to mammals. The specialized head (scolex) of
tapeworms is an adaptation for holding onto the lining of the small intestine. Look at a
scolex under the compound microscope and make a labeled sketch showing the
arrangement of hooks and suckers:
Attached to the scolex, the main body of a tapeworm consists of a tape-like ribbon of
reproductive units called proglottids. Reproduction and establishment of new individuals in
a new vertebrate host often involve complex life cycles. Having a large surface/volume
ratio as a result of being flat, and living in their hosts’ digestive tracts, nutrient acquisition is
easy for tapeworms; they lack digestive systems, absorbing nutrition by diffusion.
Station 7: Phylum Nematoda – Free-living Roundworms
One of the most successful animal phyla by whatever criterion you happen to choose for
success - number of species, number of individuals, diversity of habitat, or effect on other
living organisms - has to be phylum Nematoda. Only the arthropods exceed them in
number of known species. Nematodes are found in more locations than any other group of
multicellular animals. Most free-living nematodes are benthic animals and live in aquatic
sediments and soil in enormous numbers.
Observe the movement of “vinegar eels” in the demonstration culture; note that roundworms
are NOT flattened and NOT segmented. Describe (and/or sketch) the characteristic
movement pattern of roundworms as demonstrated by vinegar eels.
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Station 8: Phylum Nematoda – Parasitic Roundworms
There are many parasitic roundworm species of various sizes. Look at the demonstration
specimens of male and female Ascaris worms, which live as intestinal parasites. Note the
cylindrical body (unlike flatworms) and absence of segmentation (unlike earthworms).
Observe a prepared slide of muscle tissue with a cyst of Trichinella spiralis , the nematode
parasite that causes trichinosis. Study the parasite’s life cycle, and suggest ways in which
infection could be avoided.
Station 9: Phylum Mollusca – Chitons (Class Polyplacophora)
Phylum Mollusca is one of the larger animal phyla and is also one of the best known. There
are more than 100,000 described living species distributed among some very dissimilarlooking organisms such as clams, snails and octopuses – as well as the perhaps lesser
known chitons.
A chiton (not to be confused with chitin, a polysaccharide!) is a flattened marine mollusk
with a reduced shell made up of 7 or 8 overlapping plates, embedded in the mantle. The
broad foot is used to creep along slowly in the same manner as snails and to grip the
substrate, defying wave action.
Observe the chiton specimens on display and make a labeled sketch of one:
Add sketches of a few different plates, as found on the beach.
Most chiton species live in the rocky intertidal zone where they feed with a radula (a
rasping organ common in mollusks), scraping algae off the rocks. Check out the radula
under the microscope and sketch it:
Station 10: Phylum Mollusca – Class Gastropoda
Most gastropods (snails, limpets, nudibranchs, slugs, abalone), are marine, although
freshwater and terrestrial species are common. Virtually every type of feeding habit is
exhibited by gastropods. There are herbivores, carnivores, scavengers, deposit feeders,
suspension feeders, and parasites. Despite this diversity, most have a rasping feeding
organ known as radula and this has become highly specialized in many species, including
for drilling through bivalve shells in the case of carnivorous gastropods like the moon snail.
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Some, but not all, of the gastropods have shells (slugs, for example, lack shells). One
pronounced feature of this group is a distinct head with eyes at the tips of tentacles. The
muscular foot is also readily apparent and a thickened disc called an operculum is often
seen on the shelled members of this group. The operculum provides a protective door or
covering over the shell aperture when the animal retreats inside.
Sketch a snail and label the following external features: mantle, shell, foot, tentacle, eyes.
Station 11: Phylum Mollusca – Class Bivalvia
Bivalves (clams, oysters, scallops) are a group of marine and freshwater mollusks in
which the shell is laterally compressed and divided into 2 hinged valves. The hinge or
ligament connects the two valves by their “beaks” (a.k.a. umbos), which typically would
point forward, i.e. down in the case of a clam burrowing in mud or sand, so the valves are
on the animal’s left and right sides.
A muscular foot does the digging – sometimes surprisingly fast! – while siphons extend
upward for filter-feeding and respiration. Bivalves lack a radula. When burrowing clams
become dislodged, they need to be replaced in the proper orientation, since it is highly
unlikely that they could manage to turn themselves around…
Identify the following structures in the dissected clam and label them in Fig. 4 below:
Umbo, left valve, right valve, anterior adductor muscle, posterior adductor muscle,
foot, siphon, gills. Also look for the locations of mouth and anus.
Figure 4. Clam Anatomy (© Campbell, 2014, p.730)
Annual growth lines can be seen on the shells of most species and the youngest part of
the shell is the umbo adjacent to the hinge. Under a dissecting microscope, can you
determine the approximate age of a bivalve shell?
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Station 12: Key to Clams
This dichotomous key to common BC clams was developed by Dr. Bill Austin, formerly of
the Marine Ecology Station at Sidney. Use it to identify the specimens provided.
1a. External color of valves blue/black .......................................................................................................................2
1b. External color of valves white, ivory and/or tan ...................................................................................................3
2a. Valves with coarse radial ribs in places, and irregular growth lines;
fully grown typically larger than 10 cm………………………..........California Mussel (Mytilus californiensis)
2b. Valves without radial ribs, regular concentric growth lines may be present;
fully grown typically less than 7 ……………………………………..……........Bay Mussel (Mytilus trossulus)
3a. One valve flat and with a large hole in it ................................................... ….Alaska Jingle (Pododesmus cepio)
3b. Both valves convex and without holes [unless drilled] .........................................................................................4
4a... Valves irregularly roughened and frilly ................................................. Giant Pacific Oyster (Crassostrea gigas)
4b. Valves smooth or regularly sculptured, not frilly .................................................................................................5
5a. Cancellate sculpture [Both concentric and radial] ................................................................................................6
5b. Sculpture radial OR concentric OR absent ...........................................................................................................7
6a. Inside of valves with teeth on lower margin, no purple stain on
interior posterior margin [tend to be ovoid]…………………………….Native Littleneck (Protothaca staminea)
6b. Inside of valves without teeth on lower margin, a purple stain on
interior posterior margin [tend to be elongate]………...................................Japanese Littleneck or Manila Clam
(Venerupis philippinarum)
7a. Strong radial sculpture [no concentric sculpture] ..... …Nuttal’s Cockle or Heart Cockle (Clinocardium nuttalli)
7b. Concentric sculpture or smooth ............................................................................................................................8
8a. With a chondrophore [shelf perpendicular to one valve below the beak] ............. Softshell Clam (Mya arenaria)
8b. No chondrophore ..................................................................................................................................................9
9a. Posterior [pointed end] of both valves bent to right viewed from above ....Bent-nose Macoma (Macoma nasuta)
9b. Posterior end of valves not distinctly bent to right.............................................................................................. 10
10a. Valves tend to be rectangular and with large posterior gape almost equal
to height of shell ....................................................................................................... Geoduck (Panopea abrupta)
10b. Valves tend to be oval and posterior gape, if present,
about 1/3 height of shell ...................................................................................................................................... 11
11a. Black/brown ligament forms external hump, no posterior gape ................... Butter Clam (Saxidomus giganteus)
11b. Ligament without hump, posterior gape about 1/3 height of shell ............................. Horse Clam (Tresus capax)
Terminology: cancellate: lattice-like
chondrophore: process on interior umbo that supports the hinge function
Key out these mollusk species:
A = __________________
B = __________________
C = __________________
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Kingdom Animalia: Porifera, Cnidaria, Platyhelminthes, Nematoda and Mollusca
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Station 13: Phylum Mollusca – Class Cephalopoda
Cephalopods (octopuses, squids, nautiluses) are marine predators with well-developed
eyes and brains. The head projects into a crown of large prehensile arms and tentacles.
Most have a beak made of keratin as well as a radula.
Nautiluses have an external shell, squid have a reduced, internal shell, and octopuses lack
a shell. Octopuses are intelligent invertebrates with individual personalities, capable of
complex social interactions, memory, learning, problem-solving and play. Many are
capable of camouflage, some even of mimicking other sea creatures!
In the dissected squid, identify the following features: arm, tentacle, eye, fin, excurrent
siphon, gill, rectum, anus, ink sac, gonads and label them in Fig. 5 below:
Fig. 5. Squid Anatomy
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