Is heelsplitter the name of a muscle in your foot or is it a mussel? How about triceps, wartyback, deltoids, monkeyface, biceps, pocketbook, quadriceps, papershell, tibialis, pigtoe, gluteus maximus, sheepnose, sartorius, catspaw, trapezius, lilliput, soleus, or mucket? Can you pick the mussels from the muscles?
Chances are you might be much more familiar with the names of your muscles than with these freshwater mussels. Don’t be disappointed if you don’t know much about mussels. They spend their lives partially or wholly buried in permanent bodies of water. The vast majority are found in streams while some are found in ponds or lakes.
So what is a mussel? Mussels are bi-valve mollusks with elongated shells and are cousins to the squid, octopus, nautilus, snail, and slug. They are an important source of food for fish, raccoons, muskrats, otters, turtles, and waterfowl. Some may refer to the generic term clam when they find a shell on the river bank or happen across a live mussel. Although both are bi-valve mollusks, the clam and mussel are of different species. So a clam is not a mussel and a mussel is not a clam.
A mussel possesses an incurrent siphon and an excurrent siphon. To obtain food, it draws water through the incurrent siphon where it filters out microscopic plant and animal material suspended in the water. Waste is then discharged through the excurrent siphon.
Most freshwater mussel species are of separate sexes. The male releases sperm into the water which enters the female through the incurrent siphon where the eggs are fertilized. The fertilized eggs develop into an intermediate larval stage (called glochidia) and are stored in the female’s gills. In spring or summer, the glochidia are expelled and seek out a host to parasitize. Depending on the species of mussel the glochidia are either internal parasites or external parasites. The host is usually a fish and the glochidia form cysts on either the gills or fins of their host.
While in the cyst, the glochidia change form and begin to resemble mussels. They then break free of the cyst and drop to the stream or lake bottom to begin independent lives. The period of attachment lasts from 1 to 25 weeks depending on a variety of factors including the host, location of attachment and water temperature. Mussels are long-lived with some reported to have survived over 100 years.
Unfortunately, many are endangered and others have been extirpated. According to the 2010 Wildlife Diversity Report published by the Indiana Department of Natural Resources, freshwater mussels are the most endangered group of animals in Indiana. Historically, 77 species were found in the state. Of these, 19 are completely gone or no longer producing. Currently, there are 24 species in Indiana listed as state or federally endangered or of special concern.
Threats to the state’s mussel population include overharvesting, pesticides, herbicides, and other chemicals, run-off, siltation, poor land management practices, and competition from exotic species such as the zebra mussel. Quite a number of foes are arrayed against our mussels.
So let’s put our muscles to work and protect our mussels. Support clean-up efforts, wise land management practices, and protection of our streams and lakes.
A few more of the common names of our freshwater muscles…
Spectacle case • Washboard • Pistolgrip • Winged Mapleleaf • Rabbits Foot • Fatmucket
Pimpleback • Threeridge • Wabash Pig-toe • Ebonyshell • Rayed bean • Elephant-ear
Spike • Pondhorn Floater • Elktoe • Rock-pocketbook • Kidneyshell • Bleufer • Fanshell Purple wartyback • Butterfly • Hickorynut • Deertoe • Fawnsfoot • Fat Pocketbook
Higgins eye • Snuffbox • Ring Pink • Pyramid pigtoe • Rainbow • Creeper • PeeWee
Purple Warty Back Muscle
Source: Field Guide to Freshwater Mussels of the Midwest, Cummings, Kevin S. and Christine A. Meyer, Illinois Natural History Survey, 1992.