Cyclonaias tuberculata
purple wartyback

The purple wartyback is found in the Mississippi drainage, the Lake St. Clair drainage, the Detroit River and Lake Erie.

In Michigan C. tuberculata is mainly found in rivers of the Lake Erie drainage and the Kalamazoo, St. Joseph, Thornapple and Grand Rivers of the Lake Michigan drainage. It has also been recorded in the Menominee River in the upper peninsula. (Burch, 1975; van der Schalie, 1938)

Cyclonaias tuberculata is mainly found in rivers where definite riverine conditions with a stronger current exist. In Michigan and Ohio it may be found in smaller rivers. In the St. Joseph River, it was found in slower moving waters that were fairly clear. In general the purple wartyback is found in better quality streams. (Badra, 2004; van der Schalie, 1938; Watters, 1995)

The purple wartyback is up to 12.7 cm (5 inches) long , and is round. The shell is fairly thick, heavy and compressed. The anterior end is rounded, the posterior end somewhat angled. The dorsal margin is straight to slightly rounded and the ventral margin is broadly rounded.

Umbos are low and only slightly raised above the hinge line. The beak sculpture has several wavy ridges.

The periostracum (outer shell layer) has several pustules, and ridges on the dorsal wing. Younger specimens are yellowish to greenish brown, while older specimens tend to be more uniformly brown.

On the inner shell, the left valve has two widely divergent, serrated , thin and low pseudocardinal teeth. The two lateral teeth are striated, and straight to slightly curved. The right valve has one heavy, triangular serrated pseudocardinal tooth with a small tooth on either side. The right, single lateral tooth is slightly curved and striated.

The beak cavity is very deep. The nacre is almost always purple, and rarely white.

In Michigan, this species can be confused with the pimpleback. The pimpleback usually has a prominent green ray, lacks a dorsal wing and purple nacre. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

Fertilized eggs are brooded in the marsupia (water tubes) up to three months, where they develop into larvae, called glochidia. The glochidia are then released into the water where they must attach to the gill filaments and/or general body surface of the host fish. After attachment, epithelial tissue from the host fish grows over and encapsulates the glochidium, usually within a few hours. The glochidium then metamorphoses into a juvenile mussel within a few days or weeks. After metamorphosis, the juvenile is sloughed off as a free-living organism. Juveniles are found in the substrate where they develop into adults. (Arey, 1921; Lefevre and Curtis, 1910)

The age of mussels can be determined by looking at annual rings on the shell. However, no demographic data on this species has been recorded.

Mussels in general are rather sedentary, although they may move in response to changing water levels and conditions. Although not thoroughly documented, the mussels may vertically migrate to release glochidia and spawn. Often this species is buried under the substrate. (Oesch, 1984)

The middle lobe of the mantle edge has most of a bivalve's sensory organs. Paired statocysts, which are fluid filled chambers with a solid granule or pellet (a statolity) are in the mussel's foot. The statocysts help the mussel with georeception, or orientation.

Mussels are heterothermic, and therefore are sensitive and responsive to temperature.

Unionids in general may have some form of chemical reception to recognize fish hosts. How the purple wartyback attracts or if it recognizes its fish host is unknown.

Glochidia respond to touch, light and some chemical cues. In general, when touched or a fluid is introduced, they will respond by clamping shut. (Arey, 1921; Brusca and Brusca, 2003; Watters, 1995)

In general, unionids are filter feeders. The mussels use cilia to pump water into the incurrent siphon where food is caught in a mucus lining in the demibranchs. Particles are sorted by the labial palps and then directed to the mouth. Mussels have been cultured on algae, but they may also ingest bacteria, protozoans and other organic particles.

The parasitic glochidial stage absorbs blood and nutrients from hosts after attachment. Mantle cells within the glochidia feed off of the host’s tissue through phagocytocis. (Arey, 1921; Meglitsch and Schram, 1991; Watters, 1995)

Unionids in general are preyed upon by muskrats, raccoons, minks, otters, and some birds. Juveniles are probably also fed upon by freshwater drum, sheepshead, lake sturgeon, spotted suckers, redhorses, and pumpkinseeds.

Unionid mortality and reproduction is affected by unionicolid mites and monogenic trematodes feeding on gill and mantle tissue. Parasitic chironomid larvae may destroy up to half the mussel gill. (Cummings and Mayer, 1992; Watters, 1995)

Fish hosts are determined by looking at both lab metamorphosis and natural infestations. Looking at both is necessary, as lab transformations from glochidia to juvenile may occur, but the mussel may not actually infect a particular species in a natural situation. Natural infestations may also be found, but glochidia will attach to almost any fish, including those that are not suitable hosts. Lab transformations involve isolating one particular fish species and introducing glochidia either into the fish tank or directly inoculating the fish gills with glochidia. Tanks are monitored and if juveniles are later found the fish species is considered a suitable host.

In lab trials, Cyclonaias tuberculata metamorphosed on the black bullhead the yellow bullhead the channel catfish and the flathead catfish. These species generally co-exist with the purple wartyback, but no natural infestations have been observed. (Cummings and Watters, 2004; Hove et al., 1994; Hove, 1997; Hove, M.C., Engelking, R.A., Peteler, M.E et al., 1997)

There are no significant negative impacts of mussels on humans.

Mussels are ecological indicators. Their presence in a water body usually indicates good water quality.

Cyclonaias tuberculata is listed as Endangered in Wisconsin, Threatened in Illinois, Iowa and Minnesota, and Significantly Rare in North Carolina. In Michigan it is listed as Special Concern. The IUCN Red List considers this species Lower Risk, Near Threatened. (Hove, 2004)