Lampsilis siliquoidea
fatmucket

The fat mucket is found from the Mississippi River drainage from New York to Minnesota. It occurs south to Arkansas but does not occur from the Tennessee and Cumberland River systems. In the St. Lawrence River system it is found in the Canadian Interior Basin. Lampsilis siliquoidea is also found in Montana and eastern Colorado.

In Michigan L. siliquoidea is found in drainages throughout the state, both in the upper and lower peninsulas. (Burch, 1975)

Although found in various substrates and in various habitats from lakes, and headwaters to medium sized rivers, the fat mucket is usually found in quiet water on sandy-mud bottoms. Occasionally it is found in riffles, but usually in waters below riffles, or slowly running water with fine gravel, sand and mud. (Cummings and Mayer, 1992; van der Schalie, 1938; Watters, 1995)

The fat mucket is up to 12.7 cm (5 inches) long , and is oblong to elliptical in shape. The shell thickness is uniform, and may be thin to thick. This species is sexually dimorphic. Depending on habitat, sex, and age, the shell can be compressed or inflated. The anterior end is rounded, the posterior end bluntly pointed in males or truncated in females. The dorsal margin is straight and the ventral margin is straight and may be rounded.

Umbos are broad and raised only slightly above the hinge line. The beak sculpture is fine, with six to ten double-loops.

The periostracum (outer shell layer) is yellow to yellow-brown with green rays. Older specimens tend to be darker and brownish.

On the inner shell, the left valve has two pseudocardinal teeth, which are erect and compressed. The two lateral teeth are thin, short and slightly curved. The right valve has one large, erect pseudocardinal tooth. Anterior to this tooth is a smaller (lamellar) tooth. The one lateral tooth is thin and straight.

The beak cavity is shallow to moderately deep. Although the nacre is white, occasionally it is has a pink or salmon tint and iridescent posteriorly.

In Michigan, this species can be confused with the mucket and pocketbook. The mucket is generally more compressed and slightly more elliptically shaped. The pocketbook is more roundly shaped and has higher umbos. (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.

A female Lampsilis siliquoidea has a mantle flap which resembles a minnow or darter. The mimic fish lures its host fish,which chews on the flap and breaks the membrane of the gills. As a result, the fish is infected with glochidia. (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. While the fat mucket has a fish lure to attract its host fish, if or how it recognizes a specific 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 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.

The main hosts of Lampsilis siliquoidea are in the family Centrarchidae. Natural infections and glochidial metamorphosis have been observed on bluegill, black crappie, largemouth bass, walleye, white crappie and the yellow perch. Glochidial metamorphosis has also been observed on the longear sunfish, bluntnose minnow, sand shiner, sauger and smallmouth bass. (Coker et al., 1921; Cummings and Watters, 2004; Howard, 1922; O'Dee and Watters, 2000; Trdan, 1981)

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.

Lampsilis siliquoidea is currently not listed for conservation status. However, it is commonly found in lakes, where zebra mussels have been thriving.

Lampsilis siliquoidea is synonomous with Lampsilis radiata siliquoidea, and is sometimes called Lampsilis radiata.