Quadrula quadrula

The mapleleaf is found in Mississippi River drainage north to the Red River of the North and Nelson River. It is also found in the Great Lakes, south to the Gulf drainages in the Alabama river and some streams of eastern and central Texas.

In Michigan Q. quadrula has been recorded in the Black and Galien Rivers on the western side of the state as well as the Grand River. It has also been collected in the Cass and Saginaw Rivers, Saginaw Bay, and Lake Erie. (Burch, 1975)

Quadrula quadrula is mainly a large river and large lake species found in various substrates, including mud, gravel and sand. (Cummings and Mayer, 1992; Watters, 1995)

The mapleleaf is up to 10.2 cm (four inches) long , and is quadrate. The shell is usually fairly thick, heavy and partly inflated. The anterior end is broadly rounded, the posterior end rounded above the dorsal margin. The dorsal margin is straight and the ventral margin is nearly straight, or arched near the posterior end. The sulcus, a furrow that radiates from the umbo, often has bumps on the ridges.

Umbos are low, being raised only slightly above the hinge line and directed forward. The beak sculpture has raised nodules, with double-looped ridges.

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

On the inner shell, the left valve has two pseudocardinal teeth, which are heavy, large, erect and triangular. The two lateral teeth are straight, striated, and moderately long. The right valve has one large, erect triangular pseudocardinal tooth. Anterior to this tooth is a smaller (lamellar) tooth. The one lateral tooth is long and straight. The interdentum (the area between the pseudocardinal and lateral teeth) is broad.

The beak cavity is deep and the nacre is white and iridescent posteriorly.

In Michigan, this species can be confused with the pimpleback. The pimpleback is more rounded and doesn’t have a distinct sulcus. In younger specimens the pimpleback has a distinct thick green ray. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)

Fertilized eggs are brooded in the marsupia (water tubes) up to three 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.

Quadrula quadrula is probably a short term brooder, mating in early summer and releasing glochidia in late summer. (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 mapleleaf attracts or if it recognizes its host fish 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.

Glochidial metamorphosis of Quadrula quadrula has been observed on the channel catfish. (Schwebach, M., D. Schriever, et al., 2002)

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

Because of its thick and sturdy shell, Quadrula quadrula is harvested for use by the pearl industry. The shell is sliced and then ground into beads (called "slugs") which are placed in pearl producing oysters. The oysters secrete a nacre over the slugs. The finished pearl has a nucleus of freshwater mussel shell and an outer layer from the saltwater oyster.

There are no significant negative impacts of mussels on humans.

Quadrula quadrula is not on any conservation status list.

Because of shell variations, Quadrula quadrula was formerly considered to be several species.