Elliptio complanata
eastern elliptio

Mainly an Atlantic coast species, the eastern ellliptio is found in the Apalachicola river system, Altamaha River system of Georgia north to the St. Lawrence River system of Canada. In the Interior Basin it is found west to Lake Superior and within the Hudson Bay drainage.

In Michigan E. complanata is found from Cheboygan County north through the upper peninsula. In the lower peninsula the southernmost records were from Lake Huron. One historical record was from the Clinton River. (Burch, 1975; Matteson, 1948b; Matteson, 1948c)

The eastern elliptio is mainly found in stable shoals of lakes or river-lakes in the northern part of the lower peninsula and the upper peninsula. It was most abundant in substrates composed of clay mixed with marl and fine sand, but rarely in mud. Depths where it seemed most common were one to 1.6 m (3 to 5 feet). (Matteson, 1948a; van der Schalie, 1938)

The eastern elliptio is up to 12.5 cm (5 inches) long , and is quadrate or rectangular in shape. The shell is heavy and compressed with an angular posterior ridge and prominent posterior slope. The anterior end is rounded, the posterior end rounded to bluntly pointed. The dorsal margin is straight and the ventral margin is straight to slightly curved.

Umbos are low, being raised only slightly above the hinge line. The beak sculpture has 5-6 ridges.

The periostracum (outer shell layer) is tan or brown, sometimes with green rays. Older specimens tend to be more brown or black.

On the inner shell, the left valve has two pseudocardinal teeth, which are triangular and rough. The two lateral teeth are straight to slightly curved and moderately long. The right valve has one triangular, rough pseudocardinal tooth, and one straight to slightly curved, long, lateral tooth.

The beak cavity is shallow. The nacre is purple, rose-colored or white.

In Michigan, this species can be confused with the spike. The eastern ellipse is slightly more rhomboidal, more compressed, and has a slightly more prominent posterior ridge. (Cordeiro, 2003; Nedeau, McCollough, and Swartz, 2000)

Fertilized eggs are brooded in the marsupia (water tubes) up to one months, depending on environmental conditions, 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. The glochida 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; Matteson, 1948a)

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. Often they are found buried under the substrate. (Oesch, 1984)

Three large, distinct ganglia make up the bilateral nervous system of a bivalve. Cerebropleural ganglia are anterior and give rise to the visceral (gut) ganglia and pedal (foot) ganglia.

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.

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 snuffbox attracts its main fish host, the logperch, is unknown. However, the mantle flaps are darkened and may resemble food for the logperch.

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. (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.

Lab metamorphosis and natural infections of Elliptio complanata have been observed for the yellow perch and the banded killifish,.

In lab trials, Elliptio complanata metamorphosed on the green sunfish, the largemouth bass, the orangespotted sunfish, and the white crappie. (Cummings and Watters, 2004; Lefevre and Curtis, 1912; Matteson, 1948a; Matteson, 1955; Tedla and Fernando, 1969; Young, 1911)

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

This species is not on any federal or state lists.

Elliptio complanata is synonomous with Elliptio complanatus.

An detailed life history of this species was done by Max Matteson in the early 1940s in northern Michigan. (Matteson, 1948a)