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 scaleshell attracts its fish host is unknown, but females may be sacrificed to infect the host fish.
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
Leptodea leptodon is a federally Endangered species in the United States. The scaleshell is also considered Lower Risk, near Threatened on the IUCN Red List.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: lower risk - near threatened
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, Leptodea leptodon glochidia metamorphosed on the freshwater drum.
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.
Plant Foods: algae; phytoplankton
Other Foods: detritus ; microbes
Foraging Behavior: filter-feeding
Primary Diet: planktivore ; detritivore
The scaleshell historically was found in the upper Mississippi river drainage south to the Tennessee River. States where it occurred include Alabama, Arkansas, Illinois, Indiana, Iowa, Kentucky, Minnesota, Mississippi, Missouri, Ohio, Oklahoma, South Dakota, Tennessee and Wisconsin. The present distribution is within the Mississippi River in Missouri, Oklahoma and Arkansas.
In Michigan, two specimens were recorded from the Grand River. However, attempts to find this species again have been unsuccessful. Some biologists feel the historical occurrence of this species in Michigan is doubtful.
Biogeographic Regions: nearctic (Native )
The clubshell is typically found in riffles, usually in unpolluted waters with a good current. Sunstrates it inhabits are usally gravel. In Ohio, it was found on muddy bottoms of larger rivers.
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 scaleshell is up to 10.2 cm (4 inches) long , and is elongate and oblong in shape. The shell is usually fairly thin and compressed. The anterior end is rounded, the posterior end a round point. The dorsal margin is straight and the ventral margin is straight to slightly rounded.
Umbos are low, even or slightly raised above the hinge line. The beak sculpture is fine, with four or five double-looped ridges.
The periostracum (outer shell layer) is smooth, yellow to yellow-green with green rays.
On the inner shell, the left valve has one pseudocardinal teeth, which is reduced to a small, thickened ridge. The two lateral teeth are low, indistinct, and moderately long. The right valve has one pseudocardinal tooth, also reduced to a small thickened ridge. The lateral tooth is low, single, and straight.
The beak cavity is shallow or absent. The nacre is pinkish-white or light purple, rose in the umbo area, and is iridescent throughout.
In Michigan, this species can be confused with the fragile papershell. The fragile papershell is more oval, less elongate, and generally has a more pronounced dorsal wing.
Range length: 10.2 (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.
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.
Average gestation period: 10 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)
