Molluscs

A highly diversified and abundant group of organisms found in all environments
Geologic Range: Cambrian to Recent

Important molluscan groups include the following:

1. Bivalves: Marine invertebrates with two shells which are mirror images of the other (a modern example is a clam)
   Geologic Range: Ordovician to Recent
   
   
2. Cephalopods: A highly efficient group of marine predators which include the modern-day octopus, squid, and chambered nautilus
   
   Fossil cephalopods include:
   
   Ammonoids: Coiled marine predators dominant in Mesozoic seas
   
   Belemnoids: Nektic marine predators similar in appearance to the modern-day squid
   
   Nautiloids: Extremely successful straight-chambered predators dominant in the lower Paleozoic
   
   
3. Gastropods: An abundant and diverse group of shelled invertebrates found virtually in all environments (a modern example is the snail)
   Geologic Range: Cambrian to Recent
   

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