Some of the finest pearls have come from certain tributaries of the Ohio and Tennessee Rivers where conditions seem ideal for luster and translucence. Only a dozen or more of the several dozen species of mussels in the Mississippi valley have the thick white shells used for making buttons. Watch a mussel, lying on its side in shallow water, get up on edge and crawl. Shaped like a human tongue, this foot can be extended into a long finger-like tip. This tip is worked into the sand for 2 or 3 inches, then the foot contracts, raising the mussel on edge and moving it forward.
Mussels grow very slowly.
Their ages can be told by growth rings on the shell. Most commercial varieties get to be 15 or more years old and the three-ridges may live to 35 or 40 years. Most mussels shed eggs or partially developed young to carry on a free existence, but the young of several species pass through a parasitic stage attached to the gills or skin of fish. There are two sexes but the difference is important only to another clam. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.