Molluscs

SummaryPeople often associate the animal phylum ‘Mollusca’ with their most species-rich or popular subgroups: gastropods (snails, whelks, slugs, and limpets), bivalves (mussels and clams), and cephalopods (the pearl boat Nautilus, sepias, squids and octopuses, and the many fossil ammonites and belemnites). Of these, the gastropods, with more than 100,000 extant species, comprise about 80% of all molluscs and are by far the most diverse group within the phylum. The remaining classes, the aplacophoran Solenogastres (or Neomeniomorpha) and Caudofoveata (or Chaetodermomorpha), the Polyplacophora (chitons), Monoplacophora (or Tryblidia or Tergomya), and Scaphopoda (tusk-shells), are known to a much lesser extent (Box 1), but add significantly to the variability of the molluscan bauplan and to our understanding of molluscan phylogeny and evolution