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Nature Notebook – Fingernail Clams

Many times, our pond study specimens are rather shy as they sit in our collecting trays. The fingernail clam pictured below, however, was quite the showoff.

Fingernail clams are mollusks with two shells; they are also known as bivalves. The name is a good indication of their size and color. The adults, with their little pink or grayish shells, are the smallest of the bivalves. Ironically, their eggs and juveniles are the largest.

The pale tissue protruding from the shell is the clam’s foot. It is used to push the clam along the substrate or into the substrate for feeding. Clam are excellent burrowers and this habit allows them to survive drought periods as long as several months.

Two tube-like siphons form a feeding tube for the clam. Tiny hairs with the structure called cilia beat together to create a current that moves water into the tube. Minute pieces of food are absorbed into the tissues and the stream moves out the opposite siphon.

The tiny clams can travel long distances to new homes by attaching themselves to animals such as adult aquatic insects, salamanders and water birds. Occasionally a duck’s stomach becomes the mode of transportation. The clam travels, alive and undigested, until the duck relieves itself.