- Kingdom: Animalia
- Phylum: Mollusca
- Norwegian: bløtdyr
Mollusks come in many different shapes. Among the common features are a mantle with shells, plates or just calcareous spicules, covering the dorsal part (the back) of the body. A fold in the mantle forms a significant body cavity, exposed to air or water, depending on the habitat. Mollusks have two pairs of main nerve cords.
Mollusca is the largest marine phylum, including almost a fourth of all known marine species. The phylum includes ten classes, of which two are extinct. The sea snails and sea slugs, Gastropoda , is by far the largest marine class. The cuttlefish, octopuses and squids (Cephalopoda) are among the neurologically advanced and probably most intelligent invertebrates. Scallops, mussels, clams and oysters are all bivalves (Bivalvia). Another common marine class of mollusks is Polyplacophora - the chitons. Over the last couple of hundred years, there has been considerable confusion among scientists regarding classification and naming of the marine mollusks. You may still encounter the same name for different species in different publications.