Invertebrates

Sponges Sessile body consisting of canals and pores; lack tissues and organs; filter feeders. Collar cells, spicules, amoeboid cells

Cnidarians True tissues; two tissue layers; tentacles; threadlike stinging structures called nematocysts; food digested in gastrovascular cavity; radially symmetrical; some have alternating body forms (polyp and medusa); divide into three classes based on life cycle and body form. Examples: Hydras, jellyfish, sea anenomes and corals.

Flatworms Three tissue layers-- ectoderm, endoderm, and mesoderm; bilaterally symmetrical; distinct head end; parasitic and free-living forms. Phylum divided into three classes: Planarians, tapeworms, liver fluke.

Roundworms Tissues derived from ectoderm, endoderm, and mesoderm; simplest organisms to have complete digestive system from mouth and anus; divide into two classes: Rotifera, Nematoda (roundworms). Also include the tardigrades (water bears)

Segmented Worms Body made up of segments; three body layers derived from ectoderm, endoderm, and mesoderm; tube-within-a-tube body plan; divided into three classes--class Earthworms, marine worms, and leeches.

Mollusks Soft bodied invertebrates; muscular foot; mantle that often secretes a hard, calcified shell; body of most adult mollusks; many with a radula; bilaterally symmetrical; unsegmented body. Phylum divided into four classes: Clams, snails, squids, chitons.

Echinoderms Spiny-skinned marine invertebrates; bony plates form endoskeleton; radially symmetrical; water-vascular system used for locomotion, tube feet; divided into five classes.

Arthropods Segmented body; many species divided into head, thorax, and abdomen; exoskeleton of chitin covering body; periodic molting; paired, jointed appendages.