Phylum Platyhelminythes. Platyhelminthes ~ 20,000 extant species Parasitic + free-living Unsegmented flatworms.
Phylum: Mollusca Class: Polyplacophora Class: Bivalvia Class: Gastropoda Class: Cephalopoda.
Review of Animal Phylogeny. Sponges Anatomy of a Sponge.
