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 clubshell recognizes and/or attracts 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
Pleurobema clava is a federally Endangered species in the United States. The IUCN Red List considers this species Critically Endangered. The range of the clubshell has probably been reduced about 95% and this species is likely sensitive to siltation.
US Federal List: endangered
CITES: appendix ii
IUCN Red List of Threatened Species: critically endangered
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 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.
In lab trials, Pleurobema clava glochidia metamorphosed on the central stoneroller, striped shiner, logperch and blackside darter.
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 clubshell was historically found in the Ohio, Cumberland and Tennessee River systems and Lake Erie drainages. Within these river systems it was found in the Wabash, Kanawha, Kentucky, Green, Monogahela and Alleghany Rivers. The range of P. clava has been greatly reduced.
In Michigan P. clava is restricted to the St. Joseph River (of the Maumee drainage) in Hillsdale County.
Biogeographic Regions: nearctic (Native )
Pleurobema clava is found in streams and small rivers, in well oxygenated riffles with coarse sand and gravel and little silt. In Michigan, runs where it was found had water currents of 0.06-0.25 meters per second.
Habitat Regions: freshwater
Aquatic Biomes: rivers and streams
The clubshell can live up to 50 years.
Range lifespan
Status: wild: 50 (high) years.
The northern clubshell is up to 7.6 cm (3 inches) long , and is triangular and elongate in shape. The shell is usually fairly thick, and compressed to moderately inflated. The anterior end is rounded, the posterior end bluntly pointed. The dorsal margin is curved and slanted to the posterior end and the ventral margin is straight to slightly curved.
Umbos are low, being raised only slightly above the hinge line, and are situated at or near the anteriror end. The beak sculpture has concentric ridges at the tip of the umbo, and is not always visible.
The periostracum (outer shell layer) is yellow-brown with prominent broken green rays. Older specimens tend to be more brown or black.
On the inner shell, the left valve has two pseudocardinal teeth, which are small, triangular, serrated and erect. The two lateral teeth are straight to slightly curved, thin, and moderately long. The right valve has one large, erect triangular serrated pseudocardinal tooth and one lateral tooth that is also straight to slightly curved, thin and moderately long.
The beak cavity is shallow to moderately deep. The nacre is white and iridescent at the posterior end.
In Michigan, this species can be confused with the ellipse or the Wabash pigtoe. The ellipse is more compressed and has a more broadly rounded anterior end. The Wabash pigtoe lacks green rays and is also not as wedge-shaped as the clubshell.
Range length: 7.6 (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.
Pleurobema clava is a short-term brooder. Gravidity has not been recorded, so general spawning time is unknown.
Breeding interval: The clubshell breeds once in the warmer months of the year.
Breeding season: In Michigan, the breeding season is unknown.
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)
