List of animal phyla
Mollusca: a great phylum by number of species and by variety of body forms; largely aquatic. Hugely important fossil record from the Lower Cambrian. A major food source for mankind, second only to fish. United by their mantle, the muscular 'foot', the radula (teeth band), and (ancestrally) by the shell. Number of living species estimated as 50,000 to 150,000. Classes: lesser classes are the Aplacophora, Monoplacophora, and Polyplacophora. Major classes are the Gastropods, Cephalopods, Bivalves and Scaphopods. A familiarity with bivalve evolution is valuable for identifying strata, so common are their fossils. Larvae are trochophores; or veligers (many gastropods & bivalves); glochidium (some freshwater bivalves).