Lasmigona compressa

The creek heelsplitter is found in the Canadian Interior Basin, the upper Mississippi, Ohio and St. Lawrence River systems extending from Saskatchewan to Nebraska and eastward to Vermont and Quebec. It is always found from the Hudson River system in New York.

In Michigan this species is found in creeks, headwater streams and small rivers throughout drainages in the lower and upper peninsula. (Burch, 1975; van der Schalie, 1938)

The creek heelsplitter can be found throughout a watershed, but is usually in creeks and headwaters of small to medium rivers. Substrates where it has been found include fine gravel or sand.

On the Huron River, the creek heelsplitter commonly inhabited pools above and below riffles with compact sand and gravel, or mud patches near shore. In larger rivers it occupied soft mud bottoms in slow-moving currents near the edge of the river. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

The creek heelsplitter is up to 8 cm (4 inches) long , and elongate-oval in shape. The shell is usually fairly thin and compressed. The anterior end is broadly rounded, the posterior end bluntly pointed and square at the tip. The posterior ridge is prominenet and the slope is formed into a small, sculptureless wing. The dorsal margin is straight and the ventral margin is rounded to straight.

Umbos are low, being raised only slightly above the hinge line. The beak sculpture has heavy, double-loops.

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

On the inner shell, the left valve has two pseudocardinal teeth, which are long, thin, and nearly separated. The anterior pseudocardinal tooth is low and small and the posterior tooth is elevated and flared upaward. The two lateral teeth are short and thin. The right valve has one low, elongated pseudocardinal tooth. Anterior to this tooth is a smaller ridge-like tooth on the hinge line. The one lateral tooth is short, thin, and nearly parallel with the hinge line.

The beak cavity is shallow. The nacre is white, occasionally with a pink or salmon tint.

In Michigan, this species can be confused with the fluted-shell. The fluted-shell lacks lateral teeth and has flutes on the wing. (Cummings and Mayer, 1992; Parmalee, 1967; 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)

Age to sexual maturity for this species is unknown. Unionids are gonochoristic (sexes are separate) and viviparous. The glochidia, which are the larval stage of the mussels, are released live from the female after they are fully developed.

In general, gametogenesis in unionids is initiated by increasing water temperatures. The general life cycle of a unionid, includes open fertilization. Males release sperm into the water, which is taken in by the females through their respiratory current. The eggs are internally fertilized in the suprabranchial chambers, then pass into water tubes of the gills, where they develop into glochidia.

Lasmigona compressa is a long-term brooder. In the Huron River in Michigan, it was gravid from early August to late May. It probably spawns from June to July in Michigan. (Lefevre and Curtis, 1912; Watters, 1995)

Females brood fertilized eggs in their marsupial pouch. The fertilized eggs develop into glochidia. There is no parental investment after the female releases the glochidia.

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. How the creek heelsplitter attracts and/or 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. (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 transformations 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, Lasmigona compressa glochidia metamorphosed on several fish species. However, no natural infestations have been observed. Fish species where glochidia metamorphosed include the black bullhead, the yellow bullhead, flathead catfish, shortnose gar, black crappie, bluegill, green sunfish, orangespotted sunfish, smallmouth bass, brassy minnow, creek chub, mimic shiner, emerald shiner, spotfin shiner, longnose dace, gizzard shad, brookstickleback, yellow perch and slimy sculpin. (Hove, et al., 1995; McGill, et al., 2002)

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

There are no significant negative impacts of mussels on humans.

Lasmigona compressa is listed as Threatened in Iowa and Special Concern in Minnesota. (Hove, 2004)