| Term | Definition |
|---|
| invertebrate | animal that does not have a backbone |
| radial symmetry | body plan in which body parts repeat around the center of the body |
| bilateral symmetry | body plan in which only a single, imaginary line can divide the body into 2 equal halves |
| cephalization | concentration of sense organs & nerve cells at the front of an animal's body |
| spicule | spike-shaped structure that makes up the skeletons of harder sponges |
| larva | immature stage of an organism that looks different from the adult form |
| gemmule | group of archaeocytes surrounded by a tough layer of spicules; produced by some sponges |
| polyp | sessile stage of the life cycle of a cnidarian; cylindrical body with armlike tentacles |
| medusa | mobile stage of the life cycle of a cnidarian, has a bell-shaped body |
| hydrostatic skeleton | layers of circular & longitudinal muscles, together with the water in the gastrovascular cavity, that enable movement |
| coelom | fluid-filled body cavity lined with mesoderm |
| hermaphrodite | individual that has both male & female reproductive organs |
| septum | internal wall between the segments of an annelid's body |
| seta | bristle attached to the segments of many annelids |
| crop | part of the digestive system in which food can be stored |
| gizzard | part of the digestive system in which food is ground into smaller pieces |
| mantle | thin layer of tissue that covers most of a mollusk's body |
| shell | structure in mollusks made by glands in the mantle that secrete calcium carbonate |
| radula | tongue-shaped structure used for feeding by snails & slugs |
| siphon | tubelike structure through which water enters & leaves a mollusk's body |
| exoskeleton | external skeleton; tough external covering that protects & supports the body of many invertebrates |
| chitin | complex carbohydrate found in the exoskeletons of arthropods |
| appendage | structure, such as a leg or antenna, extending from the body wall |
| spiracle | small opening located along the side of the body through which air enters & leaves |
| book lung | organ with layers of respiratory tissue for exchange of gases |
| molting | process of shedding an exoskeleton & manufacturing a larger one to take its place |
| incomplete metamorphosis | type of insect development; all stages of life cycle look similar |
| complete metamorphosis | type of insect deveropment; larvae look & act completely different from parents |
| nymph | immature form that lacks functional sex organs & other adult structures |
| pupa | stage of metamorphosis in which an insect changes from larva to adult |
| society | group of closely related animals of the same species that work together for the benefit of the group |
| caste | group of individual insects specialized to perform particular tasks, or roles |
| pheromone | specific chemical messenger; affects behavior or development of other individuals of same species |
| endoskeleton | structural support located inside the body of an organism |
| tube foot | suction-cuplike structure attached attached to radial canals of echinoderms, used to walk & to open shells |
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