Tusk snails are tiny but attract big interest


POSTED: Monday, March 29, 2010

My latest passion is looking up the seashells I find on the beach, then reading about the snails that created and lived in these curly, pearly homes. This pastime, I've discovered, is just as much fun going the other way.

While paging through my identification books, I find shells I never knew existed and look up the snail's story. Finding one of these unknowns is exciting.

“;Oh!”; I think, rushing to examine the shell. “;I read about these!”;

I'm hoping that one day I'll have such a eureka moment over an Indian money tusk shell.

The tusk snail family consists of about 350 species of burrowing snails. Their name comes from their resemblance in shape and color to elephant tusks—long, narrow and mostly yellow or white. (One exception in the Indian Ocean is a brilliant jade green.)

But these tusks snails are tiny. The largest lives in Japan's waters, growing to 6 inches long, and the smallest is a Florida native only one-eighth inch long.

Unlike the solid tusks of elephants, walruses and wild boars, tusk snail shells are tubes, open at both ends. The larger end of the shell contains both the head and the foot.

The snail spends its life head down in the sand, digging with its muscular, cone-shaped foot in the same manner as clams. The snail digs until just the tip of its rear end protrudes from the sand's surface.

The head of a tusk snail is a short stub with no eyes and no chemical receptors that help some snails find food. It does, however, have a mouth and a remarkable way of eating.

Tusk snails' favorite meals are forams, tiny bottom creatures also enclosed in shells. A tusk snail's head sends out several threadlike tentacles, each with a sticky knob on the tip.

The tentacles poke around in the sand, capturing forams and other minuscule animals. If the captured prey is small, the tentacles move it to the mouth on wiggling hairs. When the prey is too large for this conveyor belt type of transport, the tentacle contracts and pops the morsel directly into the mouth, where the tusk snail chews it up with its large flat teeth.

A tusk snail's body takes up the length of its shell, but there's space inside for water to move in and out through the end of the shell sticking from the sand. This current brings in oxygen and flushes out carbon dioxide and digestive wastes. Water enters the shell slowly, taking about 10 minutes for a full inhalation. The snail exhales it all in one big whoosh.

Tusk snails are born either male or female and stay that way. Males shower the water with sperm, but females expel only one egg at a time. The eggs that are fertilized turn into tiny swimming snails that don't resemble adult tusks in the least until they stop swimming and settle down.

The Indian money tusk snail that captured my interest ranges from Alaska to Southern California and lives buried in sand and mud in waters 6 to 500 feet deep. Its Latin species name, pretiosum, means precious, a name given it from the value the Nookka Indians of Vancouver Island placed on the species. These native North Americans used the 1- to 2-inch-long shells as currency and also wore them as pricey jewelry, often in white, spiky necklaces.

This seashell currency spread east to the Dakotas, and the demand by the Plains Indians became so great, traders imported tusk snail shells native to New England.

Tusk shells might not be money anymore, but mine, when I find it, will be a treasure.

Susan Scott can be reached at