| A | B |
|---|
| blastula | embryonic stage in most animals consisting of a single layer of cells surrounding a hollow cavity |
| gastrula | embryonic stage following the blastula that has as inner and outer cell layer |
| larva | immature form of an animal that looks different from the adult form |
| metamorphosis | complete change of body form in some animals from a larva to an adult |
| invertebrate | member of a group of animals without a backbone |
| vertebrate | animal with a backbone |
| sponge | member of a group of animals that lack true tissues and organs |
| collar cell | flagellated cell in a sponge's inner layer |
| amoebocyte | cell found in sponges and other animals that may digest and distribute food, dispose of wastes, and change into other cell types |
| sessile | anchored in place |
| cnidarian | member of a group of invertebrates with radial symmetry and tentacles with stinging cells |
| radial symmetry | body plan in which an organism can be divided into equal parts around a central axis |
| cnidocyte | specialized cell in cnidarians that functions in defense and capturing prey |
| nametocyst | stinging capsule found in a cnidocyte |
| gastrovascular cavity | digestive sac |
| polyp | cnidarian body form consisting of a clindrical body with tentacles radiating from one end |
| medusa | cnidarian body form that is umbrella-shaped with fringes of tentacles |
| flatworm | member of a group of small, leaflike, or ribbon-like invertebrates that includes planarians |
| bilateral symmetry | body plan in which an animal can be divided into two equal sides |
| roundworm | member of a group of cylindrical invertebrates with pointed heads and tapered tails |
| complete digestive tract | continuous digestive tube with a separate mouth and anus |
| rotifer | meber of a group of invertebrates with a complete digestive tract and a crown of rotating cilia |
| annelid | segmented worm |
| closed circulatory system | blood transport system in which blood remains enclosed in vessels; and nutrients, oxygen, and wastes diffuse through vessel walls |
| acoelomate | aniam lacking a body cavity |
| pseudocoelom | fluid-filled internal space that is in direct contact with the wall of the digestive tract |
| coelom | fluid-filled body cavity completely lined by a layer of mesoderm cells |
| mollusk | member of a group of invertebrates characterized by a muscular foot and a mantle |
| mantle | body surface outgrowth that drapes over a mollusk |
| radula | scraping organ characteristic of mollusks |
| open circulatory system | blood transport system in which blood is pumped into chamers where it comes in direct contact with tissues and organs |
| gastropod | member of a group of mollusks that includes snails and slugs |
| bivalve | member of a group of mollusks with hinged shells, such as clasm, mussels, scallops, and oysters |
| cephalopod | member of a group of mollusks that includes squids and octopuses |
| echinoderm | member of a group of marine invertebrates that includes sea urchins and sea stars |
| endoskeleton | skeleton located inside the body; characteristic of all vertebrates and some invertebrates |
| water vascular system | in echinoderms, a network of water-filled canals that function in movement, food gathering, and as a basic circulatory system |
| tube feet | in echinoderms, structures that are part of the water vascular system and function in locomotion, feeding, and gas exchange |
| protostome | member of a group of organisms with a coelom that develops from a solid cell mass in the embryo, such as mollusks, annelids, and arthropods |
| deuterostome | member of a group of organisms that includes echinoderms and chordates in which the coelom forms from part of the early embryo's digestive tube |
| Cambrian explosion | burst of diverse animal species originating during the Cambrian period |
