| A | B |
|---|
| mollusk | a soft-bodied invertebrate that usually has a hard shell, such as a snail. |
| mantle | in a mollusk, the thin layer of tissue that covers the soft body; it secretes chemicals that become a shell or protects the body if no shell exists. |
| gill | organ that exchanges carbon dioxide with water. |
| open circulatory system | a type of blood-circulation system that lacks vessels but instead bathes internal organs in blood, such as in mollusks. |
| radula | in gastropods, a tongue-like organ with rows. |
| closed circulatory system | a type of blood-circulation system in which vessels transport blood to the internal organs, as in humans. |
| setae | in a segemented worm, bristle-like structures on the outside of the body that help it grip soil and move. |
| crop | in an earthworm, a sac in the digestive system that stores soil. |
| gizzard | in an earthworm, a muscular digestive structure that grinds soil. |
| Arthropoda | largest animal phylum, classified by the number of body segements and appendages; includes insects, shrimp, spiders, and centipedes. |
| appendage | a strucutre growing from the body, such as an arm or leg. |
| exoskeleton | on all arthropods, the hard, lightweight external covering that shields, supports, and protects the body. |
| molting | the periodic shedding and replacing of the old, outgrown body covering, such as skin or an exoskeleton. |
| spiracle | in an arthropod, openings in the abdomen and thorax through which air enters and waste gases leave. |
| metamorphosis | the changes in the body form during the life cycle- for example: egg, larva, pupa, adult. |
| pesticide | a chemical that kills undesirable plants or animal pests. |
| echinoderm | a spiny-skinned invertebrate that lives on the bottom of the ocean and that moves by means of a water-vascular system. |
| water-vascular system | in echinoderms, the network of water-filled canals to which thousands of tube feet are connected. |
| tube feet | in echinoderms, the structures act like suction cups and help the sea star move and feed. |
