| A | B |
|---|
| bilateral symmetry | two sides of the body mirror each other |
| radial symmetry | body is organized around a center |
| asymetrical | body that has no symmetry |
| nerve cords | packs of neurons that carry messages on a single path |
| ganglion | a mass of nerve cells |
| gut | the digestive tract |
| brain | an organ that controls nerves throughout the body |
| pores | holes on the outside of a sponge's body |
| collar cells | filter and digest food |
| osculum | hole at the top center of a sponge where water is ejected |
| regenerate | to grow a new body part |
| spicules | hard fibers that make up the skeleton of the sponge |
| cnidarians | invertebrate organisms that have stinging cells |
| medusa | body form of a cnidarian that are free floating or unattached |
| polyp | cnidarian body form that is attached to a surface |
| parasite | organism that invades and feeds on the body of another |
| host | living organism that is home to a parasite |
| radula | tongue covered with curved teeth |
| open circulatory system | a simple heart pumps blood through blood vessels that open into sinuses |
| closed circulatory system | a heart pumps blood through a network of blood vessels in a closed loop |
| visceral mass | made up of the gills, gut, and other organs; found in the center of a mollusk |
| mantle | layer of tissue that covers the visceral mass; protects mollusk bodies that lack a shell |
| segment | any part of a larger structure, such as the body of an organism, that has a clear boundary |
| castings | earthworm waste |
| polychaetes | "many bristles"; marine worms |
| arthropod | "joint foot" |
| exoskeleton | hard, external, supporting structure |
| chitin | protein that makes up the exoskeleton |
| compound eye | an eye composed of many light detectors; can see images |
| simple eye | an eye that can only detect light |
| cephalothorax | the joined head and thorax of arachnids |
| chelicerae | clawlike mouth parts |
| metamorphosis | a phase in the lifecycle in which a rapid change takes place |
| molting | the process of shedding the exoskeleton |
| echinoderm | "spiny skinned" |
| endoskeleton | internal skeleton |
| nerve ring | circle of nerve fibers, found around the mouth |
| radial nerve | runs from the nerve ring to the tip of each arm |
| water vascular system | a system of canals filled with fluid that circulates throughout the body of an echinoderm |
| ampulla | bulb that controls fluid pressure and the tube feet |
| sieve plate | flat plate on top of the sea star |
| ring canal | part of the water vascular system that is a tube around the mouth |
