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 white heelsplitter attracts or recognizes its fish 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.
Communication Channels: chemical
Perception Channels: visual ; tactile ; vibrations ; chemical
Lasmigona complanata currently has no federal or state conservation status.
US Federal List: no special status
CITES: no special status
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.
Development - Life Cycle: metamorphosis
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.
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.
In lab trials, Lasmigona complanata metamorphosed on the banded killifish, green sunfish, orangespotted sunfish and white crappie.
Ecosystem Impact: parasite
Species Used as Host:
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.
Plant Foods: algae; phytoplankton
Other Foods: detritus ; microbes
Foraging Behavior: filter-feeding
Primary Diet: planktivore ; detritivore
The white heelsplitter is found in the upper Mississippi River drainage from Pennsylvania west to Minnesota and Iowa and south to Oklahoma and Louisiana. It is also found in the Alabama River drainage, the upper St. Lawrence River system, Lake Winnipeg-Nelson River drainage from western Ontario to Alberta.
In Michigan L. complanata is found in the lower end of various rivers, including Saginaw tributaries, the Grand and Muskegon Rivers as well as a few spots on the Kalamazoo and St. Joseph (Lake Michigan) Rivers. This species was also found in the Detroit River and the Belle, Clinton, and Huron Rivers. Historical records also show it was found in the upper peninsula, in various lakes and the Whitefish River.
Biogeographic Regions: nearctic (Native )
The white heelsplitter is usually in slower waters of medium streams and rivers, and occasionally in small tributaries. In the Huron River it was found deeper waters with sluggish currents or backwater areas. The substrate was soft mud and fine sand bottoms. This species may also be resistant to some pollutants.
Habitat Regions: freshwater
Aquatic Biomes: rivers and streams
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.
The white heelsplitter is up to 15 cm (6 inches) long , and is ovate to circular in shape. The shape generally depends on the age of the mussels and the growth of the pronounced wing. The shell is relatively thin, compressed and plate-like. The anterior end is broadly rounded, the posterior end rounded to bluntly pointed where the posterior ridge meets the margin. The dorsal margin is straight and the ventral margin is uniformly rounded.
Umbos are low, not being raised above the hinge line. The beak sculpture consists of heavy, double looped ridges.
The periostracum (outer shell layer) is smooth, except for flutes on the wing. Younger individuals may have green and brown rays and are light tan in color. Older specimens are dark brown to black.
On the inner shell, the left valve has two pseudocardinal teeth, the anterior one being low and compressed. The posterior tooth is chunky and grooved. The interdentum sometimes has a high protuberance. The lateral teeth are poorly developed and look like raised extensions of the hinge line. The right valve has one single, long, triangular grooved pseudocardinal tooth. The lateral tooth is rudimentary.
The beak cavity is shallow to moderately deep and narrow. Although the nacre is white to blue-white, occasionally it is iridescent at the posterior end.
In Michigan, this species can be confused with the pink heelsplitter and the fragile papershell. The white and pink heelsplitters are distinguished by the color of their nacre. The pink heelsplitter is also more oval in shape, has a smooth beak sculpture and the wing is not as fluted. The fragile papershell is also more oval in shape, is yellowish, and has reduced hinge teeth.
Range length: 15 (high) cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
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.
Known Predators:
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.
Lasmigona complanata is a long-term brooder. In the Huron River in Michigan, it was gravid from mid-August to early June. It probably spawns from June to early August in Michigan.
Breeding interval: The white heelsplitter breeds once in the warmer months of the year.
Breeding season: In Michigan, the breeding season is probably June to mid-August.
Range gestation period: 10 (high) months.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
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.
Parental Investment: pre-fertilization (Provisioning); pre-hatching/birth (Provisioning: Female)
