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Learn more about these bizarre, less-common, tooth-like molluscs often overlooked when examining shells washed-up on Queensland beaches.
Tusk Shells belong to the class Scaphopoda. They form a distinctive group of marine molluscs characterised among other things by their curved, tooth-like, open-ended shells. The head and foot of the animal can protrude from the wider aperture of the shell, whereas the digestive, respiratory and reproductive organs are always contained within the shell. The entire animal can retract into the shell if disturbed.
All scaphopods live buried in sand or mud. The foot digs to help find food (such as minute invertebrates) and tiny tentacles secure these food items for the radular-teeth of the mouth. At rest, oxygen-containing water is drawn into the narrow end of the shell for the gills. Although some species may reach 140mm in shell length, most species are less than 20mm long and many of these are as tiny as a rice grain. Tusk shells are not often seen living, and several inhabit water as deep as 2000 metres. Australia has just over 100 species of scaphopod or about 20% of the world’s total number (500-600 species).
These unusual-looking molluscs are generally found subtidally rather than intertidally. They live in soft sandy or muddy substrates and their small shells, if washed ashore, are more difficult to see compared with those of the more commonly encountered marine snails and bivalves.
Using minute tentacles around their foot, they sift sediment containing tiny animals such as foraminiferans, algae and detritus. This is then directed to their mouth which has a grinding radula (toothed tongue) which breaks down the food into smaller bits for digestion.
No – generally not. However, humans in the past have used their shells for other purposes. Tusk shell necklaces have been found dating back to the Bronze Age; belts and headdresses in the Middle East made 11 to 15 thousand years ago contain tusk shells; and natives of the Pacific Northwest strung them as beads and used them as money.
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