Truncilla truncata
deertoe

The deer toe is found throughout the Mississippi river system and in the the St. Lawrence system. Its range extends from western Pennsylvania to Michigan and Minnesota, south though eastern Iowa, eastern Kansas, eastern Texas, through Louisiana, Alabama and Tennessee.

In the lower peninsula in western Michigan, T. truncata is found in the Grand River system, the Kalamazoo and Black and St. Joseph (Lake Michigan) Rivers. In the southeastern part of the state it is found in Lake Erie and tributaries, including the Belle, Black, Huron, and Raisin Rivers. (Burch, 1975)

In Michigan, Truncilla truncata is generally found in Lake Erie or the lower stretches of rivers. In general it is found in lakes and medium to large rivers, usually in mud, sand and/or gravel. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

The deertoe is up to 5.1 cm (2 inches) long , and is triangular, moderately inflated, and fairly thick. The anterior end is uniformly rounded, the posterior end bluntly pointed or truncated. The dorsal margin is rounded. The ventral margin is broadly rounded, and straight to concave toward the posterior end. A shallow sulcus is anterior to the posterior ridge, which is sharply angled and prominent. Females and males are not as easily distinguished as other members of the subfamily Lampsilinae.

Umbos are prominent and raised slightly above the hinge line. The beak sculpture is fine, with three to five double-looped ridges.

The periostracum (outer shell layer) is yellow, green, to yellow-brown. Usually numerous green rays are present, varying in widths and shape. Rays may be fine broken lines or V-shaped zigzag markings. Older specimens tend to be more brown.

On the inner shell, the left valve has two pseudocardinal teeth, which are tall, rough, notched and compressed. The two lateral teeth are slightly curved, short and striated. The right valve has one erect, triangular, notched pseudocardinal tooth. Anterior to this tooth is a smaller (lamellar) tooth. The one lateral tooth is arched, high and striated.

The beak cavity is shallow. Although the nacre is white, occasionally it is has a pink or salmon tint and is iridescent at the posterior end.

In Michigan, this species can be confused with the fawnsfoot. The fawnsfoot is more elongated and has a smoother dorsal ridge. (Cummings and Mayer, 1992; Oesch, 1984; 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. How the deertoe attracts and if it recognizes its fish host is unknown.

Glochidia respond to both 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.

Lab trials have not been conducted to determine the deer toe's fish host. Natural infestations were observed for freshwater drum and sauger, but metamorphosis has not been observed on either species. (Wilson, 1916)

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.

Truncilla donaciformis is not currently considered for conservation status lists.