| A | B |
|---|
| mollusk | An invertebrate with a soft, unsegmented body; most are protected by hard outer shells. |
| gill | An organisms's breathing organ that removes oxygen from water. |
| gastropod | A mollusk with a single shell or no shell. |
| cephalopod | A mollusk with feet adapted to form tentacles around its mouth. |
| kidney | An organ that removes the wastes produced by an animal's cells. |
| radula | A flexible ribbon of tiny teeth in mollusks. |
| bivalve | A mollusk that has two shells held together by hinges and strong muscles. |
| arthropod | An invertebrate that has an external skeleton, a segmented body, and jointed attachments called appendages. |
| molting | The process of shedding an outgrown skeleton. |
| metamorphosis | A process in which an animal's body undergoes dramatic changes in form during its life cycle. |
| exoskeleton | A waxy, waterproof outer shell. |
| antenna | An appendage on the head of an animal that contains sense organs. |
| arachnid | An arthropod with only two body sections. |
| chitin | The tough, flexible material from arthropod exoskeletons are made. |
| crustacean | An arthropod that has two or three body sections, five or more pairs of legs, two pairs of antennae, and usually three pairs of appendages for chewing. |
| abdomen | The hind section of an arachnid's body that contains its reproductive organs and part of its digestive tract; the hind section of an insect's body. |
| insect | An arthropod with three body sections, six legs, one pair of antennae, and usually one or two pairs of wings. |
| complete metamorphosis | A type of metamorposis characterized by four dramatically different stages: egg, larva, pupa, and adult. |
| gradual metamorphosis | A type of metamorphosis in which an egg hatches into a nymph that resembles an adult, and which has no distinctly different larval stage. |
| camoflage | Protective coloration; a common animal defense. |
| thorax | An insect's mid-section, to which its wings and legs are attached. |
| pupa | The second stage of complete metamorphosis, in which an insect is enclosed in a protective covering and gradually changes from a larva to an adult. |
| nymph | A stage of gradual metamorphosis that usually resembles the adult insect. |
| echinoderm | A radially symmetrical invertebrate that lives on the ocean floor and has a spiny internal skeleton. |
| water vascular system | A system of fluid-filled tubes in an echinoderm's body. |
| endoskeleton | An internal skeleton. |
