Actinonaias ligamentina

The mucket is found in the Mississippi River drainage from New York through Wisconsin, and from Minnesota south through eastern Texas and Alabama. In the St. Lawrence drainage, it is found in tributaries from Lake Michigan to Lake Ontario.

In Michigan this species is found in rivers in the lower peninsula, as far north as the Muskegon, Cass, and Chippewa Rivers. Historically it was common on the Grand River and its drainages. The mucket was also fairly common in rivers of the Lake Erie drainage, including the Huron, Raisin, and Clinton Rivers. (Burch, 1975)

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

The mucket grows up to 15 cm (six inches), and is elongate and oval in shape. The shell is usually fairly thick, heavy and compressed. The anterior end is rounded, the posterior end bluntly pointed. The dorsal margin is slightly curved and the ventral margin is broadly round.

Umbos are low, being raised only slightly above the hinge line. The beak sculpture is fine, with double-looped ridges, which are more visible in younger specimens.

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

On the inner shell, the left valve has two pseudocardinal teeth, which are heavy, large, and serrated. The two lateral teeth are straight to slightly curved, thin, and moderately long. The right valve has one large, erect triangular serrated pseudocardinal tooth. Anterior to this tooth is a smaller (lamellar) tooth. The one lateral tooth has fine striations.

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

In Michigan, this species can be confused with the fat mucket, Lampsilis siliquoidea. Actinonaias ligamentina tends to be more elliptical and compressed than L. siliquoidea. The umbos of L. siliquoidea are generally higher and the hinge line is not as heavy as in A. ligamentina. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

Fertilized eggs are brooded in the marsupia (water tubes) for 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 the glochidium, usually within a few hours. Each 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)

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.

In the Huron River, the mucket was gravid from early August to mid-June. As a long-term brooder, it will release its glochidia and then spawn in the summer. (Lefevre and Curtis, 1912; van der Schalie, 1938; 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. Mantle flaps in the lampsilines are modified to attract potential fish hosts. How the mucket attracts or 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 fish, including 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.

Both lab transformations and natural infections have been observed on the green sunfish, white crappie, smallmouth bass, largemouth bass, sauger, yellow perch and the white bass.

Lab transformations only have been observed on the banded killifish, central stoneroller, silverjaw minnow, black crappie, orange spotted sunfish, rock bass and Tippecanoe darter. These species generally coexist with Actinonais ligamentina. (Cummings and Watters, 2004; Lefevre and Curtis, 1912)

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.

Actinonaias ligamentina is does not have any federal status, but is listed as endangered in Kansas and threatened in Minnesota. (Hove, 2004)

Actinonaias ligamentina was formerly known as Actinonaias carinata.