Carolina Heelsplitter

The first recorded encounter with the Carolina heelsplitter was in 1852 by Isaac Lea. He described this new creature as Unio decoratus. The largest recorded specimen was about 5 in (130 mm) long. This freshwater mussel has a greenish-brown to dark brown outer shell; the inner shell usually has nacre that is pearly white or bluish-white, although it can be pale orange in older specimens. The younger individuals tend to have faint black or greenish-brown rays on the outer surface of the shell. This medium-sized mussel has well-developed, but thin, lateral teeth that are somewhat delicate. The Carolina heelsplitter also has two blade-like pseudocardinal teeth in the left valve, and one in the right valve. With an "ovate, trapezoid-shaped, unsculptured shell", the size of the largest Carolina heelsplitter is about 4.6 inches (12 cm) in length and 1.56 inches (4.0 cm) in width, with a thickness of 2.7 inches (6.9 cm).

The Carolina heelsplitter lives in shallow streams and rivers, and occasionally, ponds. They can usually be found in mud or mixed sediments, usually along stable stream banks, but have also been found in the middle of a waterway. The water must not carry much sediment. Historically, the Carolina heelsplitter was known to be found in the Catawba River and Pee Dee River systems in North Carolina, and the Pee Dee and Savannah River systems of South Carolina. These mussels historically lived possibly in the Saluda River systems in South Carolina. Currently, 10 known populations (prior to the 2007–2008 drought) occur in North and South Carolina. The areas include Goose Creek and Flat Creek in the Pee Dee River system, Waxhaw Creek, Sixmile Creek, Gills Creek, Fishing Creek, and Bull Run Creek in the Catawba River system, and Red Bank Creek, Turkey Creek, and Cuffytown Creek in the Saluda River system. The numbers of individuals in every population is very small:

One to 17 individuals were found in eight of the known populations, with only one to five individuals being found in four of these eight populations. In only one population, 26 individuals were found The largest population included only 42 individuals. The numbers that the surveyors found also indicate that the species is in decline, and also that none of the populations has improved over time. …

The reproductive cycle begins when a male Carolina heelsplitter releases his sperm into the stream. Soon afterward, the sperm is taken in by the females, in a process called siphoning. The female's eggs, which are carried in the female's gills, are then fertilized. The Carolina heelsplitter is a bradytichtic species, brooding fertilized eggs over the winter after spawning. When the glochidia (larvae) are fully developed the next year, the female mussel releases them into the water. The larvae must attach themselves quickly to a body part of their host fish, which is not harmed in the process. Host species for this mussel include members of the Cyprinidae. Attached to the fish, the heelsplitters receive oxygen and other needs from the host for several weeks. When they have grown into fully developed juvenile mussels, they release themselves from the fish and settle into the stream or river. A fish host is very important to all mussels, not only because it provides the young with food and oxygen, but also because it serves as a mode of transportation. The transportation of the mussels is key when attempting to create new populations in streams and river banks. Thus, this creature can seed the fresh waters and have more larvae.