| Term | Definition |
| ostia | small pores in a sponge's body where water enters through |
| oscula | large pores in a sponge's body where water exits the body |
| sessile | an organism that remains attached to a surface its entire life |
| choanocyte | unique flagellated cells with collar-like structure in sponges |
| amoebocyte | amoeba-like cell that supplies nutrition and removes waste in sponge body cells |
| spongin | flexible, structural protein fibers in the mesoglea of sponges |
| spicule | needle of silica or calcium carbonate in the skeleton of some sponges |
| gemmule | clusters of amoebocytes encased in a protective coat; produced by freshwater sponges in cold or dry weather |
| medusa | free swimming, umbrella-shaped body form of a cnidarian; jellyfish |
| polyp | pipe-shaped body form of a cnidarian usually attached to a rock or other object |
| cnidocyte | stinging cells used by cnidarians to stun prey |
| nematocyst | barbed harpoon within a cnidocyte of a cnidarian, used to spear prey |
| basal disk | the small area on a hydra that secretes a sticky substance that enables them to adhere to rocks or plants in the water |
| planula | free swimming larva that developed from cnidarian zygotes |
| proglottid | rectangular body segments on a tapeworm |
| fluke | parasitic flatworm of the phylum trematoda |
| tegument | thick protective covering of endoparasitic cells that help prevent them from being digested by their host |