Ptychobranchus fasciolaris
kidneyshell

The kidneyshell is found in the Ohio, Tennessee and Cumberland river systems. Its range stretches as far north as tributaries of Lake Erie south to Arkansas, Oklahoma, and west to Kansas.

In Michigan P. fasciolaris is found mainly in the Lake Erie drainages, and in the Saginaw River drainage. (Burch, 1975)

The kidneyshell is usually found in small to medium rivers, usually in areas with fairly good flow. In general substrates it inhabits include sand and/or gravel. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

The kidneyshell is up to 15.2 cm (6 inches) long , elongate, and kidney-shaped. The shell is usually fairly thick, solid and compressed. The anterior end is rounded, the posterior end bluntly pointed. The dorsal margin is straight to slightly curved and the ventral margin is curved, straight or arched.

Umbos are low and even with the hinge line. The beak sculpture is fine, with two to three concentric ridges, and tuberculate toward the posterior.

The periostracum (outer shell layer) is smooth, yellow to yellow-brown with broad green interrupted rays. Older specimens tend to be more brown.

On the inner shell, the left valve has two pseudocardinal teeth, which are thick, heavy, triangular, and serrated. The two lateral teeth are straight to slightly curved, heavy, and short. The right valve has one heavy, compressed, pyramidal pseudocardinal tooth. A smaller roughened tooth may be on either side. The one lateral tooth is wide, heavy, elevated and serrated.

The beak cavity is shallow or absent. Females have undulations or fold on the inside of the shell. The nacre is white and is iridescent posteriorly.

In Michigan, this species can be confused with the mucket, ellipse and rainbow. The kidneyshell generally has a heavier hinge and teeth than these species. The mucket is less elongate and more oval. The ellipse is generally smaller and has wavy green rays on the posterior half of the shell. The rainbow is also generally smaller and has a “v” shaped beak sculpture. (Cummings and Mayer, 1992; Watters, 1995)

Fertilized eggs are brooded in the marsupia (water tubes) up to 11 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 a glochidium, usually within a few hours. The glochidia 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. (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. Mantle flaps in the lampsilines are modified to attract potential fish hosts. The kidneyshell has glochidial packets which resemble larval fish or Simulidae larvae. Fish are likely attracted to these, thinking they are food. How and if the kidneyshell is able to recognize a suitable 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.

Although fish hosts for P. fasciolaris have not been tested, congeners metamorphose on both Etheostoma and Percina species. In a southeastern Michigan study, Ptychobranchus fasciolaris was significantly associated with the presence of Etheostoma caeruleum, E. blennoides and P. caprodes. These species may be potential hosts. (Barnhart and Roberts, 1997; Haag and Warren, 1997; Mulcrone, 2004)

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.

Ptychobranchus fasciolaris is Endangered in Illinois and Special Concern in Indiana. Under the Canadian federal Species At Risk Act, P. fasciolaris is listed as Endangered. (Environment Canada, 2003; Hove, 2004)