When I say I am a malacologist, I often am asked if that is a bad ecologist. No, I study the animal group Mollusca, which includes slugs, snails, sea slugs, clams, tusk shells, chitons (“coat of mail” shells), squid and octopi. Mollusks are all around us. Many people pick up shells when they go on vacation to the seashore, lake or river. We battle snails and slugs as pests in our gardens. Power plants fight the zebra mussel in water intake pipes, and many people eat escargot, calamari, mussels, clams and oysters on the half shell.
Mollusks have been used since ancient times as containers, jewelry, money, sources of dye and food. Pearls are a birthstone (June). A major gas company (Shell) uses the scallop as its icon. Mollusks are found in virtually all habitats, including the extremes of the tropics, deserts, and the Arctic – on land, in freshwater, in the oceans and even in deep-ocean thermal vents and cold seeps.
I am specifically interested in freshwater clams. Haven’t heard of them? Well, your grandmother or great-grandmother knew of them – they were used to make buttons on men’s dress shirts before World War II. Those freshwater pearl necklaces and earrings women wear came from freshwater clams. The cultured pearl industry grows pearls and harvests North American freshwater clamshells to make the plugs used as the seed for cultured pearls.
Prehistoric Native Americans modified freshwater clams as spoons, tools and ornaments. They cut them into beads and ground them up as a hardening ingredient for their pottery. Some early historical documentation indicates they dried the mollusk meat as jerky to keep for the lean parts of the year when food was scarce. Prehistorically, marine conch shells were traded from the South Atlantic Coast to the interior of eastern North America and used as large dippers; the columella (the central axis of the conch shell) was modified into earrings or hair pins. Some conch shell pieces were cut into beads to be sewn onto clothing. Smaller marine snails, such as the marginella and olives shells, were traded inland and used as jewelry.
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Perhaps surprisingly, the greatest diversity of freshwater clam species in the world is found in the southeastern United States, with Vietnam’s Mekong River basin coming in second. Freshwater clams are important indicators of stream health – the proverbial “canary in the coal mine.” Owing to the combined effects of water pollution, habitat destruction and damming of rivers, freshwater clams and freshwater snails qualify as the most endangered animal groups on the planet, with about 75 percent at some level of extinction. In North America alone, historical records document that 29 species of freshwater mussels and 67 species of freshwater snails have been lost to extinction, highlighting the urgency for increased conservation of freshwater resources.
Arthur Bogan is research curator of aquatic invertebrates at the N.C. Museum of Natural Sciences.