Molluscs (Mollusca) are a highly diverse group of animals that include cephalopods (squid, octopuses, cuttlefish), gastropods (nudibranchs, snails, slugs, limpets, sea hares), bivalves (mussels, clams, oysters, scallops) and many other groups of organisms. There are an estimated total of more than 250,000 species of molluscs.
Some of the main characteristics that define molluscs are quite technical in nature. For instance, molluscs are triploblastic. This means that during the early stages of their embryonic development molluscs have three primary germ layers (ectoderm, mesoderm, and endoderm). Molluscs are also protosomes. This means that during their development the blastopore (an opening in the primitive gut of the embryonic organism) becomes the mouth of the animal.
Members of Phylum Mollusca: The Phylum Mollusca is subdivided into the following Classes:
- Class Aplacophora (solenogasters, deep-sea wormlike creatures)
- Class Bivalvia (clams, oysters, scallops, mussels)
- Class Cephalopoda (squid, octopodes, nautilus, cuttlefish)
- Class Gastropoda (nudibranchs, snails, slugs, limpets, sea hares, sea angel, sea butterfly, sea lemon)
- Class Monoplacophora (deep-sea limpet-like creatures)
- Class Polyplacophora (chitons)
- Class Scaphopoda (tusk shells)
