shells

Mollusc shells have also had a long history of usage by mankind, many have been used as decorations, or as a substance to carve into cameos and buttons. In North America Tusk shells on the west coast and Cockles on the East supplied the basis of a system of money, in many tropical countries the shells of coweries were until recent times used extensively in trade. Pearls, which arise in oysters as a result of the oysters attempts to cover up a grain of sand within its mantle, have been and still are much sort after. The 'mother of pearl' used to make pearl buttons comes from bivalve shells and so great was the market for it that the Mississippi and Missouri river basins have been seriously over collected and the bivalves are now quite scarce. In ancient times the city of Tyre was famous for its purple dye, this dye was made from a marine mollusc called Murex sp. while Sepia, a brown pigment used by artists was, perhaps still is, made from the ink of Cuttlefish. Not all the interactions between man and molluscs are to man's benefit however, slugs and snails are, in some places, serious pests of of crops, and are often a nuisance in peoples gardens. Wooden ships and wharves can be destroyed by burrowing bivalves such as Teredo navalis, known as ship worms, which weaken the timbers until they collapse or fall apart.