Radial Symmetry- An arrangement of the body parts of an organism liek pieces of a pie around an imaginary central axis. Any slice passing longitudinally through a radially symmetric organism's central axis divides it into mirror-image halves
Bilateral Symmetry- An arrangement of body parts such that an organism can be divided equally by a single cut passing longitudinally through it. A bilaterally symmetric organism has mirror-image right and left sides.
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Body Cavity- A fluid-containing space between the digestive tract and the body wall.
Pseudocoelom- A body cavity that is not lined with mesoderm and is in direct contact with the wall of the digestive tract.
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True Coelom- A body cavity completely lined with tissue derived from mesoderm.
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Protostome- A mode of animal development in which the opening formed during gastrulation becomes the mouth. Animals with the protostome pattern of development include the flatworms, mollusus, annelids, nematodes, and arthropods.
Deuterostome- A mode of animal development in which the opening fomred during gastrulation becomes the anus. Animals with the deuterostome pattern of development include the echinoderms and the chordates.
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Phylum- In Linnaean classification, the taxonomic category above class.
True tissues- Collections of specialized cells isolated from other tissues.
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Choanocyte- A flagellated feeding cell found in sponges. Also called a collar cell, it has a collar-like ring that traps food particles around the base of its flagellum.
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Sessile- An organism that is anchored to its substrate.
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Tentacle- A slender flexible limb or appendage in an animal, esp. around the mouth of an invertebrate, used for grasping, moving about, or bearing sense organs.
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Cnidarian: An animal characterized by cnidocytes, radial symmetry, a gastrovascular cavity, and a polyp and medusa body form. Cnidarians include the hydras, jellies, sea anemones, corals, and related animals.
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Digestive Tract: Passageway of food that begins at the mouth down to the throat, esophagus, stomach, intestines, and finally to the anus.
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Nematode- A roundworm, characterized by a pseudocoelom, a cylindrical, wormlike body form, and a tough cuticle that is molted to permit growth.
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Cuticle- (1) In animals, a tough, nonliving outer layer of the skin. (2) In plants, a waxy coating on the surface of stems and leaves that helps retain water.
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Mollusc- A soft-bodied animal characterized by a muscular foot, mantle, mantle cavity, and visceral mass. Molluscs include gastropods (snails and slugs), bivalves (clams, oysters, and scallops), and cephalopods (squids and octopuses).
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Gastropod- A member of the largest group of molluscs, including snails and slugs.
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Bivalve- A member of a group of molluscs that includes clams, mussels, scallops, and oysters.
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Cephalopod- A member of a group of molluscs that includes squids, cuttlefish, octopuses, and nautiluses.
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Foot- In an invertebrate animal, a structure used for locomotion or attachment, such as the muscular organ etending from the ventral side of a mollusc.
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Visceral Mass- One of the three main parts of a mollusc, containing most of the internal organs.
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Coelom- A body cavity completely lined with mesoderm.
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Mantle- In a mollusc, the outgrowth of the body surface that drapes over the animal. The mantle produces the shell and forms the mantle cavity.
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Gill- An extension of the body surface of an aquatic animal, specialized for gas exchange and/or suspension feeding.
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Echinoderm- Member of a phylum of slow-moving or sessile marine animals characterized by a rough or spiny skin, a waster vascular system, an endoskeleton, and radial symmetry in adults. Echinoderms include sea stars, sea urchins, and sand dollars.
Homeotic Gene- A master control gene that determines the identity of a body structure of a developing organism, presumably by controlling the developmental fate of groups of cells.
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Chordata- Comprises true vertebrates and animals that have a dorsal, hollow nerve cord, a stiff longitudinal notochord, phyryngeal slits, and a muscular post-anal tail.
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Lophotrochozoans- Animals in the taxa who either develop a lohpophore or go through the trochophore larva stage
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Ecdysozoans- animals that have an exoskeleton that is a thick nonliving covering; provides protection and support, it does not grow with the organism; some exoskeletons contain chitin and the exoskeleton allows for new mechanisms for locomotion and respiration.
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