Invertebrates  The Parazoa  The Radiata  The Acoelomates  The Pseudocoelomates  The Coelomates: Protostomes  The Coelomates: Deuterostomes  1,000,000+ species of animals  95% are invertebrates  Most are aquatic

The Parazoa  Sponges  Sessile  Lack muscles and nerves  Suspension-feeders

The Radiata Cnidaria  Corals, hydras, jellyfis  Radial symmetry  Diploblastic  Gastrovascular cavity  Cnidocytes  Nerve net Ctenophora  Comb jellies  100 species, all marine

The Acoelomates  Bilateral symmetry  Moderate cephalization  Triploblastic  Organs, organ systems and muscle  Still lack a body cavity (coelom)  Flatworms  Examples: planaria, liver flukes, tapeworms

The Pseudocoelomates  Includes the phyla Rotifera and Nematoda  Complete digestive system  Fluid filled body cavity, acts as a hydrostatic skeleton

Coelomates  Two major lines: Protostomes and Deuterostomes  Probably evolved to fill different ecological niches  Differ in cleavage patterns and fate of the blastopore

The Protostomes  “mouth first”  Includes a number of phyla: nemertae, bryozoans, brachiopods, mollusks, annelids, and arthropods  Characterized by determinate cleavage  Formation of a mouth from the blastopore  Spiral cleavage

The Deuterostomes  “mouth second”  Spiral cleavage  Blastopore forms the anus  Includes echinoderms and chordates  Indeterminate cleavage