| A | B |
|---|
| Invertebrates | animals that do not have a backbone or vertebral column. |
| Vertebrates | animals who have a backbone and a vertebarl column. |
| Feedback inhibition | process by which cells release energy in the absence of oxygen. |
| Blastula | a hollow ball of cells. |
| Deuterostome | an animal whose anus is formed from which wastes leave the digestive tract. |
| Endoderm | innermost germ layer of most animals; develops into the linnigs of the disgestive tract and much of the respiratory system. |
| Anus | the opening through which wastes leave the digestive tract. |
| Mesoderm | middle germ layer of most animals; gives rise to muscles and much of the circulatory, reproductive, and excretory systems. |
| Ectoderm | outermost layer, gives rise to sense organs, nerves, and the outer layer of the skin. |
| Radial symmetry | body plan in which body parts repeat around the center of the body, characteristic of sea anemones and sea stars. |
| Bilateral symmetry | body plan in which only a single, imaginary line can divide the body into two equal halves, charcteristic of worms, arthropods, and chordates. |
| Cephalization | concentration of sense organs and nerve cells at the front of an animal's body. |
| Choanocytes | specialized cells that use flagella to move a steady current of water through the sponge. |
| Osculum | a darge hole at the top of the sopnge. |
| Spicule | a spike-shaped structure made of chalklike calium carbonate or glasslike silica. |
| Archaeoctyes | specialized cells that move around within the walls of the sponge. |
| Internal fertilization | process in which eggs are fertilized inside the female's body. |
| Larva | an immature stage of an organism that looks defferent from the adult form. |
| Gemmuels | group of archaeocytes surrounded by a tough layer of spicules; produced by some sponges. |
| Enidocytes | stringing vells, that are located along their tentacles. |
| Nematocyst | a poison-filled, stinging structure that contains a tightly coiled dart. |
| Polyp | a cylindrical body with armlike tentacles. |
| Medusa | has a motile, bell-shaped body with the mouth on the bottom. |
| Gastrovascular cavity | a digestive chamber with one opening. |
| Nerve net | a loosely organized network of nerve cells that together aloow enidarians to detect stimuli such as the touch of a foreign object. |
| Hydrostatic skeleton | consists of a layer of circular muscles and a layer of longitudinal muscles that, together with the water in the gastrovascular cavity, enable the enidarian to move. |
| External ferilization | takes place outside the female's body. |
