Tusk shell

The tusk shells or tooth shells, often referred to by the more-technical term scaphopods /ˈskæfəˌpɒd/ (Greek, "boat-footed"), are members of a class of shelled marine mollusc with worldwide distribution, and are the only class of exclusively infaunal marine molluscs. Shells of species within this class range from about 0.5 to 15 cm in length. Members of the order Dentaliida tend to be significantly larger than those of the order Gadilida..

 

These molluscs live in soft substrates offshore (usually not intertidally). Because of this subtidal habitat and the small size of most species, many beachcombers are unfamiliar with them; their shells are not as common or as easily visible in the beach drift as the shells of sea snails and clams.The shells of Dentalium hexagonum, a scaphopod mollusc, were strung on thread and used by the natives of the Pacific Northwest as shell money. Dentalium shells were also used to make belts and headdresses by the Natufian culture of the Middle East, and are a possible indicator of early social stratification..

 

Shells of the species Dentalium pretiosum were used as money..

 

Molecular data suggest that the scaphopods are a sister group to the cephalopods, although higher-level molluscan phylogeny remains somewhat unresolved. There is a good fossil record of scaphopods from the Mississippian onwards, making them the youngest molluscan class; but the origin of the group remains contentious.

 

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