| A | B |
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| mollusk | an invertebrate with a soft, unsegmented body; most are protected by hard outer shells |
| kidney | a major organ of the excretory system; eliminates urea, excess water and the other waste materials from the body |
| gill | an organism's breathing organ that removes oxygen from water |
| radula | a flexible ribbon of tiny teeth in mollusks |
| gastropod | a mollusk with a single shell or no shell |
| bivalve | a mollusk that has two shells held together by hinges and strong muscles |
| cephalopod | a mollusk with feet adapted to form tentacles around its mouth |
| anthropod | an invertebrate that has an external skeleton, a segmented body, and jointed attachments called appendages |
| exoskeleton | an outer skeleton |
| chitin | the tough, flexible, material from which arthropod exoskeletons are made |
| molting | the process of shedding an outgrown exoskeleton |
| antenna | an appendage on the head of some animals that contains sense organs |
| crustacean | an anthropod that has two or three body sections, five or more pairs of legs, two pairs of antennae and ususally three pairs of appendages for chewing |
| metamorphosis | a process in which an animal's body undergoes dramatic changes in form during its life cycle |
| arachnid | an arthropod with only two body sections |
| 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 |
| thorax | an insect's mid-section, to which its wings and legs are attached |
| complete metamorphosis | a type of metamorphosis characterized by four dramatically different stages:egg, larva, pupa, and adult |
| pupa | the second stage of the complete metamorphosis, in which an insect is enclosed in a protective covering and gradually changes from a larva to an 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 |
| nymph | a stage of gradual metamorphosis that usually resembles the adult insect |
| camouflage | protective coloration; a common animal defense |
| pheromone | a chemical released by one animal that affects the behavior of another animal of the same species |
| bioluminescence | the production of light by a living organism |
| echinoderm | a radially symmetrical invertebrate that lives on the ocean floor and has a spiny internal skeleton |
| endoskeleton | an internal skeleton |
| water vascular system | a system of fluid-filled tubes in an echinoderm's body |
