Dentaliida
Gadilida

The tusk shells are a class Scaphopoda of marine mollusks distinguished by curved tubular shells open at both ends, resembling a elephant's tusk (thus the name). They are mostly small, with some species reaching 15 centimeters long, and live in the bottom sediment where they feed on microscopic detritus and organisms such as foraminifera. The several hundred known species are found worldwide.

The mantle is entirely within the shell. The foot extends from the larger end of the shell, and is used to burrow through the substrate. A number of minute tentacles around the foot, called captacula, sift through the sediment and latch onto bits of food which they then convey to the mouth. The mouth has grinding teeth that break the bit into smaller pieces for digestion.

The scaphopid vascular system is rudimentary, lacking both heart and blood vessels; the blood is held in sinuses throughout the body cavity, and pumped by the rhythmic action of the foot.

Tusk shells are well-known in the fossil record, first appearing in the Ordovician (last of all molluscan groups).

The shells were used by the natives of the Pacific Northwest as wampum.

References

• G. Steiner, "Phylogeny and classification of Scaphopoda", Journal of Molluscan Studies 58:385-400 (1992)

External links

• The Scaphopod Page - many further links
• Ron Shimek's scaphopod page