| A | B |
|---|
| Invertebrates | Animals that lack a backbone |
| Vertebrates | Animals that possess a backbone |
| Spherical symmetry | An organism possesses spherical symmetry if it can be cut into two identical halves by any cut that runs through the organism's center. |
| Radial symmetry | An organism possesses radial symmetry if it can be cut into two identical halves by any longitudinal cut through its center. |
| Bilateral symmetry | An organism possesses bilateral symmetry if it can only be cut into two identical halves by a single longitudinal cut along its center which divides it into right and left halves. |
| Epidermis | An outer layer of cells designed to provide protection |
| Mesenchyme | The jellylike substance that separates the epidermis from the inner cells in a sponge |
| Collar cells (choanocytes) | Flagellated cells that push water through a sponge |
| Amoebocytes | Cells that move using pseudopods and perform different functions in different animals |
| Gemmule | A cluster of cells encased in a hard, spicule-reinforced shell |
| Polyp | The sessile, tubular form of a cnidarian with a mouth and tentacles at one end and a basal disk at the other |
| Medusa | A free-swimming cnidarian with a bell-shaped body and tentacles |
| Epithelium | Animal tissue consisting of one or more layers of cells that have only one free surface, because the other surface adheres to a membrane or other substance |
| Mesoglea | The jellylike substance that separates the epithelial cells in a cnidarian |
| Nematocysts | Small capsules that contain a toxin which is injected into prey or predators |
| Testes | Organs that produce sperm |
| Ovaries | Organs that produce eggs |
| Anterior end | The end of an animal that contains its head |
| Posterior end | The end of an animal that contains its tail |
| Circulatory system | A system designed to transport food and other necessary substances throughout a creature's body |
| Nervous system | A system of sensitive cells that respond to stimuli such as sound, touch, and taste |
| Ganglia (singular: ganglion) | Masses of nerve cell bodies |
| Hermaphroditic | Possessing both the male and female reproductive organs |
| Regeneration | The ability to regrow a missing part of the body |
| Mantle | A sheath of tissue that encloses the vital organs of a mollusk, makes the mollusk's shell, and performs respiration |
| Visceral hump | A hump that contains a mollusk's heart, digestive, and excretory organs |
| Foot | A muscular organ that is used for locomotion and takes a variety of forms depending on the animal |
| Radula | An organ covered with teeth that mollusks use to scrape food into their mouths |
| Univalve (sometimes called gastropod) | An organism with a single shell |
| Bivalve (sometimes called pelecypod) | An organism with two shells |
| Shell | A tough, multilayered structure secreted by the mantle, generally used for protection, but sometimes for body support |
