Major Animal Phyla
Animals are a diverse group of multicellular organisms with highly variable body plans and
ecologies. Most of the animals you know best are likely vertebrate animals. But vertebrates
constitute a relatively small part of animal diversity. All vertebrates belong to a single phylum of
animals called Chordates. In this activity we focus on some of the major animal phyla other than
Chordates – the phyla that contain invertebrate animals. While this is only a small sample of
those animals, it will show you some of the breadth of invertebrate diversity.
For each representative animal, you are given the Phylum and the Subphylum or Class to which
the animal belongs. Animals are assigned to specific phyla and classes based largely on
characteristics of their anatomy including:
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Body Symmetry
Digestive Tract Type,
Skeletal Type,
and Muscle Type.
SPONGE – PHYLUM PORIFERA
Sponges have the simplest body form of any animal. Sponges are so simple in their overall form
that they are really better thought of as highly organized colonies of individual cells rather than
true multicellular animals. Unlike other animals, sponges lack true tissues and live attached to
the ocean bottom filtering water to feed. Sponges are asymmetrical, have scattered spicules that
make up their skeleton. They have no muscles or digestive tract.
Why do you think the sponge has holes (pores)?
HYDRA – PHYLUM CNIDARIA; CLASS HYDROZOA
Cnidarians are radially symmetrical animals with stinging cells that they use for defense and to
trap prey. They have a digestive tract with only one opening that serves as both the mouth and
the anus. The hydra shows you the polyp form of a cnidarian. It is basically the shape of an
upright bag with tentacles surrounding the only opening. It sits attached to the bottom and feeds
by trapping prey with the stinging cells embedded in its tentacles. It has both circular and
longitudinal muscles and uses a gelatinous substance called mesoglea as its ‘skeleton’.
Obtain a live hydra and place it on a watch glass so that you can put it under the dissecting
microscope for observation. Try feeding your hydra some baby water fleas.
Describe the way in which it catches and eats its prey.
UPSIDE DOWN JELLYFISH – PHYLUM CNIDARIA; CLASS SCYPHOZOA
Observe the upside down jellyfish. Watch how it moves. These jellyfish have photosynthetic
algae in their tentacles that feed the jellyfish by making food from sunlight. They live upside
down in shallow waters near mangroves.
Why do you think they live in shallow water and not in deep water?
PLANARIAN – PHYLUM PLATYHELMINTHES; CLASS TURBELLARIA
Platyhelminthes are ‘flat worms’ including flukes, tapeworms, and planarians. Planarians are
bilaterally symmetrical and have a digestive tract with only one opening. They have both circular
and longitudinal muscles and use a tissue called mesoglea as their ‘skeleton’. Watch one of the
live planarians crawl in a bit of water on a watch glass under the dissecting microscope.
How would you describe its movement?
Draw one entire planarian here and label the eye spots.
CLAM WORM – PHYLUM ANNELIDA; CLASS POLYCHAETA
Annelids are bilaterally symmetrical, have a digestive tract with a separate mouth and anus, have
circular and longitudinal muscles, and use a body cavity called a coelom as their ‘skeleton’.
Annelids also have a closed circulatory system with all of the worm’s blood contained inside of
blood vessels. Polychaete annelids like the clam worm are characterized by paired appendages
called parapodia found on each body segment.
Examine the clam worm swimming. Notice that its body movement involves the propagation of
waves. The direction of propagation of the body waves is said to be ‘direct’ in Nereis as opposed
to the wave that propagates through the body of a snake or an eel which is said to be ‘retrograde’.
What do you think this means?
TUBIFEX WORMS – PHYLUM ANNELIDA; CLASS OLIGOCHAETA
The phylum Annelida, class Oligochaeta contains the common earthworm as well as other
aquatic worms such as tubifex worms. Obtain a few live tubifex worms and place them in a
watch glass. Examine them under the dissecting scope.
Can you see the setae (bristles) on the side of the worm? Draw a few segments of the live
worm showing the positions of the setae.
MEDICAL LEECH – PHYLUM ANNELIDA; CLASS HIRUDINEA
Observe the swimming and reattachment of the live leech in a small finger bowl.
Make a sketch of the leech and label the anterior and posterior suckers. What are these
suckers used for?
AQUATIC SNAIL – PHYLUM MOLLUSCA; CLASS GASTROPODA
Mollusca is the phylum that includes snails, clams, and octopus. All molluscs are bilaterally
symetrical, have a digestive tract with a mouth and anus, have circular and longitudinal muscles,
and most have a shell that protects their soft body.
The mollusc class Gastropoda includes snails and slugs. Observe the aquatic snail crawling.
Describe the way in which the snail senses its environment.
Describe the type of movement used by the snail. Does it look ‘wavelike’ – similar to the
annelids – or is it an entirely different type of movement?
COQUINAS – PHYLUM MOLLUSCA; CLASS BIVALVIA
Obtain a small dish with sand and sea water to observe the coquinas. These molluscs move very
quickly for clams. You should be able to watch them burrow in the sand. If your clams will not
burrow, roll them around vigorously in your hand to mimic the waves tossing them about on the
seashore – this induces burrowing behavior.
Describe the way in which the coquina uses its foot to burrow.
Make a simple sketch of the shape of the coquina shell. What features of the shell shape
might help the clam to bury itself rapidly?
C. ELEGANS – PHYLUM NEMATODA
Nematodes, or ‘round worms’ are bilaterally symmetrical, have both a mouth and an anus, have
only longitudinal muscles, and use a cavity called a pseudocoel as their ‘skeleton’. Parasitic
nematodes include those that cause trichinosis and heart worm infections in dogs and cats.
The free-living nematode C. elegans has been widely used as a model organism for studying
molecular and developmental biology since the early 1970s. Examine the live C. elegans under
the dissecting scope.
How is the wave it generates different from the wave generated by the clam worm?
HORSESHOE CRAB – PHYLUM ARTHROPODA; SUBPHYLUM CHELICERATA
The Phylum Arthropoda includes spiders, insects, and lobsters and has by far the most species of
any group of living things. All arthropods are bilaterally symmetrical, have a mouth and anus,
have segmented bodies with jointed appendages, and have a hard exoskeleton that they molt.
They move their joints with flexor and extensor muscles much the way that you move your
joints. The sublphylum Chelicerata includes spiders, scorpions, and horseshoe crabs (which are
not really crabs). They have no antennae, and two basic body regions (the cephalothorax and the
abdomen). They have six pairs of appendages. The first pair of appendages consists of pincerlike structures called chelicerae. Five pairs of walking legs are found posterior to the chelicerae.
At the base of the first four pairs of walking legs are structures called gnathobases used to chew
food.
On the diagrams, label the following structures; the carapace (cephalothorax), the
abdomen, the telson, the book gill, the chelicerae, the five pairs of walking legs.
CENTIPEDE AND MILLIPEDE – PHYLUM ARTHROPODA; SUBPHYLUM MYRIAPODA
Summarize the key characteristics that distinguish a centipede from a millipede.
Centipede
Millipede
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diet: ______________________________
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diet: ______________________________
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# of appendage pairs per segment: ______
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# of appendage pairs per segment: ______
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shape of segment in cross section:
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shape of segment in cross section:
____________________________
____________________________
CRICKET – PHYLUM ARTHROPODA; CLASS INSECTA
Insects are the only invertebrates that are able to fly. We will use a cricket as an example of an
insect.
How many body segments are there in the cricket? ___________ How many pairs of
antennae? ___________ How many pairs of wings? ___________ How many pairs of
walking legs? ___________
How can you tell a male cricket from a female cricket?
On this diagram label: the antennae, the compound eyes, the walking legs, the wings, and
the ovipositor.
CRAYFISH AND GHOST SHRIMP – PHYLUM ARTHROPODA; SUBPHYLUM CRUSTACEA
The order Decapoda which includes most of the crustaceans you know well such as crabs, sand
fleas, shrimp, and lobsters have five pairs of walking legs.
Observe a live ghost shrimp. How do you think the ghost shrimp senses objects in its
surroundings?
Observe the live crayfish. On the diagram label: the two pairs of antennae, the
cephalothorax, the abdomen, and the walking legs.
TUXEDO URCHIN – PHYLUM ECHINODERMATA; CLASS ECHINOIDEA
Echinoderms include starfish and sea urchins. They are the invertebrate animals that are most
closely related to the phylum that includes vertebrates (Chordates). As adults they have a form of
radial symmetry called ‘pentaradial’ because the body is divided into five roughly equal parts.
They have a mouth and an anus, circular and longitudinal muscles, and an internal skeleton made
up of bony plates called ossicles.
Examine the live sea urchin. Notice the tube feet and spines. Does it appear that each spine
and tube foot moves independently or do they seem to have coordinated movement?
STARFISH – PHYLUM ECHINODERMATA; CLASS ASTEROIDEA
SERPENT BRITTLE STAR – PHYLUM ECHINODERMATA; CLASS OPHIUROIDEA
Examine the live starfish and serpent brittle star. Their endoskeletons are made up of individual
ossicles similar to the ossicles that make up the test of the urchin. The oral side of these animals
is facing down. Carefully turn the animals onto their aboral surface. You should see the tube feet
lining the ambulacral grooves which radiate along each arm away from the mouth in the middle
of the central disc.
How do you think these animals feed?