All terms in this list:

symmetry: arrangement if individual body parts; can be radial (arranged around a central point), bilateral ( mirror-image body parts), of asymmetrical (no define body shape)

invertebrate: an animal without a backbone

cnidarian: radially symmetrical, hollow-bodied animal with two cell layers organized into tissues

polyp: vase-shaped, usually sessile bady formed in the life cycle of a cnidarian

medusa: free-swimming, bell-shaped body form in the life cycle of a cnidarian

mollusk: soft-bodied, bilaterally symmetrical invertebrate with a large, muscular foot, a mantle, and an open circulatory system; usually has a shell

mantle: thin layer of tissue that covers a molluskś body and that can secrete a shell

gill: organ that allows a water-dwelling animal to exchange carbon dioxide for dissolved oxygen in the water

radula: scratchy, tonguelike organ in many mollusks that has rows of teethlike projections used to scrape and grate food

open circulatory system: a type of bloodcirculation system that lacks blood vessels and in which blood washes over the organs

closed circulatory system: a type of blood-circulation system in which blood is transported through blood vessels rather than surrounding the organs

arthropod: bilaterally symmetrical animal with jointed appendages, a protective exoskeleton, and a segmented body

appendage: structure such as a claw, leg, or antenna that grows from the body

exoskeleton: rigid, protective body covering of an arthropod that supports the body and reduces water loss

metamorphosis: change of body form that can be complete or incomplete