Key Features of Animals ingest food multicellular no cell walls classified largely based on: body symmetry digestive tract type skeletal type muscle type

FIGURE 23-1 An evolutionary tree of some major animal phyla

FIGURE 23-2a Body symmetry and cephalization (a) Animals with radial symmetry lack a well-defined head. Any plane that passes through the central axis divides the body into mirror-image halves.

Blind Digestive Tract with Mouth/Anus Open Digestive Tract with Mouth and Anus

Hydrostatic Skeleton Exoskeleton Endoskeletons

Circular and Longitudinal Muscles move Elongated Bodies Flexors and Extensors move Jointed Skeletons

Porifera asymmetrical body plan lack true tissues and organs internal skeleton made of spicules

Cnidaria radial symmetry jellylike mesoglea bag-like digestive tract with a single opening tentacles equipped with stinging cells

Platyhelminthes bilateral symmetry digestive tract with a single opening mesenchyme tissue

Annelida bilateral symmetry digestive tract with two openings (mouth and anus) coelom functions as a skeleton longitudinal and circular muscles body segmented closed circulatory system

Mollusca bilateral symmetry soft body usually with a shell digestive tract with two openings circular and longitudinal muscles

Nematoda bilateral symmetry digestive tract with separate mouth and anus longitudinal muscles only

Arthropoda bilateral symmetry paired, jointed appendages body divided into segments exoskeleton which must be molted flexor and extensor muscles

Echinodermata adults have pentaradial symmetry possess an endoskeleton that sends projections through the skin unique tube foot locomotory system