Vertebrate: animal with backbone.

Invertebrate: animals without a backbone.

 Symmetry: the balanced arrangement o body parts around a center point or along a center line.

 Sponge: simple invertebrates tha have pores.

 Pore: small opening.

 Stinging- cell animals: animals with stinging cell and hollow, saclike bodies that lack organs.

 Tentacle: armlike part of a stinging-cell animal.

 Flatworm: simplest worm with flattened body.

 Tapeworm: a kind of flatworm with a flattened, ribbonlike body divided into sections.

Cyst: a young worm with a protective covering.

 Planarian: a common freshwater flatworm that is not a parasite.

 Roundworm: worm that have long bodies with pointed ends.

 Hookworm: roundworm that is a parasite to humans.

Anus: opening through which undigested food leaves the body.

 Segmented worm: worms with body divided into sections called segments.