A mussel is a relatively simple animal enclosed by two shells connected by a ligament. The shells are formed largely out of calcium carbonate that has been extracted from the waters where mussels live. The calcium carbonate is then deposited in successive layers. The hard shell provides some protection for the inner animal. Internally, the body consists of gills for breathing, a digestive tract for processing food, a large muscular foot for locomotion, and mantle tissue that produces the shell.

Freshwater mussels are extremely variable with respect to life span, coloration, and size. For example, some species live for only 10 years and others may live for as long as 100 years.

Shell color can range from yellow to green to brown to black and may contain bumps, tubercles, and ridges or can remain very smooth. Species range in size from only one inch to over one foot. Thin-shelled species like the giant floater and fragile papershell grow much faster than thicker-shelled species like the threeridge and mapleleaf. Mussels have very colorful common names such as monkeyface, threehorn wartyback, rough pigtoe, spike, and pink heelsplitter.

Freshwater mussels have a unique life cycle. Unlike oysters and clams, most freshwater mussels need a fish to complete their life cycle. Some mussels require a specific host fish to complete their life cycle; others can use a variety of fish species. For more information on host fish, click here. In the wild, male mussels release sperm into the water column. The sperm are drawn into the female as she filters water for food. The fertilized eggs reside within pouches (marsupia) of the modified gills and develop into larvae termed glochidia--tiny creatures that are parasitic and must find a suitable fish host to complete their life cycle.

Glochidia are triangular, spherical, or hatch-shaped and range in diameter from 0.08 to 0.35 millimeters. A single female can carry from a few thousand to several million glochidia.