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 rayed bean 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.
Communication Channels: chemical
Perception Channels: visual ; tactile ; vibrations ; chemical
Villosa fabalis is a federal candidate species being considered for listing in the United States. Currently it is listed as endangered in Michigan, Ohio, and New York. Indiana lists the rayed bean as Special Concern.
In Canada, V. fabalis is endangered under the Species At Risk Act.
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.
While freshwater mussels require a host fish for metamorphosis, the host fish for V. fabalis has not been determined.
Ecosystem Impact: parasite
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 rayed-bean is found in sporadic in the Ohio River drainage north to Lake Erie drainages in Michigan and Ontario, and in the Duck and the upper Tennessee Rivers.
In Michigan V. fabalis is found in the Detroit River, Lake Erie and its tributaries.
Biogeographic Regions: nearctic (Native )
The rayed bean is found in lakes and small to large streams. Substrates in inhabits include mud, sand and gravel. This species may also be associated with water willow stands.
In the Clinton River headwaters the rayed bean was found buried in sand among aquatic vegetation roots in about four inches of flowing water. It seems more common in lake plain areas of the Lake Erie basin where substrates are finer.
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 rayed bean is up to 3.8 cm (1.5 inches) long , and is elongate in shape. The shell is usually fairly thick, solid and moderately inflated. The anterior end is rounded, the posterior end 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 two or three heavy ridges, knobbed posteriorly.
The periostracum (outer shell layer) is smooth except for growth lines. The shell is green, yellowish-green or brown with numerous dark green wavy rays. Older specimens tend to be more brown.
On the inner shell, the left valve has two pseudocardinal teeth, which are triangular, heavy, large and rough. The two lateral teeth are short, low and heavy. The right valve has one triangular, heavy, large pseudocardinal tooth. Sometimes small tubercular teeth are on either side of this psuedocardinal tooth. The one lateral tooth is also short, low, and heavy.
The beak cavity is shallow. The nacre is white and is iridescent at the posterior end.
In Michigan, this species can be confused with the lilliput and the rainbow. Both the lilliput and rainbow are thinner and have more delicate hinge and teeth. The lilliput is slightly more cylindrical. The rainbow is larger, has more yellowish coloring and more prominent green rays.
Range length: 3.8 (high) cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes shaped differently
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.
Villosa fabalis is a long-term brooder, and was gravid in the Huron River from mid-August to the following spring in late May. This species probably spawns from June to July in Michigan.
Breeding interval: The snuffbox mussel breeds once in the warmer months of the year.
Breeding season: In Michigan, the breeding season is mid-July to 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)
Villosa fabalis, the rayed bean, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.
This species lives in eastern North America. It is native to the drainages of the Ohio River, the Tennessee River, and the Great Lakes.
The Canadian Species at Risk Act listed it in the List of Wildlife Species at Risk as being endangered in Canada.[2]
Villosa fabalis, the rayed bean, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.
