| Term | Definition |
|---|
| sessile | organism that is permanently attached to a surface |
| symmetry | a term that describes the arrangement of body structures |
| radial symmerty | an animal's body plan that can be divided along any plane, through a central axis, into roughly equal halves |
| bilateral symmetry | animals with a body plan that can be divided down its length into two similar right and left halves that form mirror images of each other |
| anterior | head end of bilateral animals where sensory organs are often located |
| posterior | tail end of bilaterally symmetric animals |
| dorsal | upper surface of bilaterally symmetric animals |
| ventral | lower surface of bilaterally symmetric animals |
| coelom | fluid-filled body cavity completely surrounded by mesoderm |
| exoskeleton | hard covering on the outside of some animals, including spiders and mollusks; provides a framework for support, protects soft body tissues, and provides a place for muscle attachment |
| invertebrate | animal that does not have a backbone |
| filter feeding | method in which food particles are filtered from water as it passes by or through some part of the organism |
| polyp | a cnidarian body form that is tube-shaped with a mouth surrounded by tentacles |
| medusa | a cnidarian body form that is umbrella-shaped with tentacles that hang down |
| nerve net | simple netlike nervous system in cnidarians that conducts nerve impulses from all parts of the cnidarian's body |
| nephridia | organs that remove metabolic wastes from an animal's body |
| mantle | a membrane that surrounds the internal organs of mollusks; in mollusks with shells, it secretes the shell |
| radula | in some snails and mollusks, the rasping, tonguelike organ used to drill, scrape, grate, or cut food |
| setae | tiny bristles that help segmented worms move by anchoring their bodies in the soil so each segment can move the animal along |
| gizzard | sac with muscular walls and hard particles that grind soil before it passes into the intestine; common in birds and annelids such as earthworms |
| appendage | any structure, such as a leg or antenna, that grows out of an animal's body |
| molting | in arthropods, the periodic shedding of an old exoskeleton |
| spiracle | in arthropods, openings on the thorax and abdomen through which air enters and leaves the tracheal tubes |
| mandible | in most arthropods. mouthparts adapted for holding, chewing, sucking, or biting various foods |
| metamorphosis | in insects, series of chemically-controlled changes in body structure from juvenile to adult; may be complete or incomplete |
| larva | in insects, the free-living, wormlike stage of metamorphosis, often called a caterpillar |
| pupa | stage of insect metamorphosis where tissues and organs are broken down and replaced by adult tissues; larva emerges from pupa as a mature adult |
| nymph | stage of incomplete metamorphosis where an insect hatching from an egg has the same general appearance as the adult insect but is smaller and sexually immature |
| tube foot | in echinoderms, hollow, thin-walled tubes that end in a suction cup; part of the water vascular system, they also aid in locomotion, gas exchange and excretion |
| ray | long tapered arms of some echinoderms that are covered with short, rounded spines |
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