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. (Burch, 1975; Szymanski, 1998)
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. (Cummings and Mayer, 1992; Watters, 1995)
- Habitat Regions
- Aquatic Biomes
- rivers and streams
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. (Cummings and Mayer, 1992; Oesch, 1984; Watters, 1995)
- Sexual Dimorphism
- sexes alike
- Range length
- 10.2 (high) cm
- 4.02 (high) in
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. (Arey, 1921; Lefevre and Curtis, 1910)
- Development - Life Cycle
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. (Lefevre and Curtis, 1912; Watters, 1995)
- Key Reproductive Features
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- 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
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
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.
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. (Oesch, 1984)
Communication and Perception
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.
- Communication Channels
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)
- Plant Foods
- Other Foods
- Foraging Behavior
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)
- Known Predators
- muskrat, Ondatra zibethicus
- mink, Neovison vison
- raccoon Procyon lotor
- otter, Lontra canadensis
- turtles, Testudines
- hellbenders, Cryptobranchus
- freshwater drum, Aplodinotus grunniens
- sheepshead, Archosargus probatocephalus
- lake sturgeon, Acipenser fulvescens
- shortnosed sturgeon, Acipenser brevirostrum
- spotted suckers, Minytrema melanops
- common red-horse, Moxostoma
- catfish, Siluriformes
- pumpkinseed, Lepomis gibbosus
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.
- Ecosystem Impact
- freshwater drum, Aplodinotus grunniens
Economic Importance for Humans: Positive
Mussels are ecological indicators. Their presence in a water body usually indicates good water quality.
Economic Importance for Humans: Negative
There are no significant negative impacts of mussels on humans.
is a federally Endangered species in the United States. The scaleshell is also considered Lower Risk, near Threatened on the IUCN Red List.
Renee Sherman Mulcrone (author).
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- bilateral symmetry
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
an animal that mainly eats decomposed plants and/or animals
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- internal fertilization
fertilization takes place within the female's body
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
- native range
the area in which the animal is naturally found, the region in which it is endemic.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats plankton
- seasonal breeding
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. J. Exp. Zool., 33: 463-499.
Barnhart, C., F. Riusech, M. Baird. 1998. Drum is host of the scaleshell, Leptodea leptodon. Triannual Unionid Report, 16: 35. Accessed October 04, 2005 at http://ellipse.inhs.uiuc.edu/FMCS/TUR/TUR16.html#p29.
Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..
Burch, J. 1975. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America. Hamburg, Michigan: Malacological Publications.
Cummings, K., C. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Champaign, Illinois: Illinois Natural History Survey Manual 5. Accessed August 25, 2005 at http://www.inhs.uiuc.edu/cbd/collections/mollusk/fieldguide.html.
Lefevre, G., W. Curtis. 1912. Experiments in the artificial propagation of fresh-water mussels. Proc. Internat. Fishery Congress, Washington. Bull. Bur. Fisheries, 28: 617-626.
Lefevre, G., W. Curtis. 1910. Reproduction and parasitism in the Unionidae. J. Expt. Biol., 9: 79-115.
Meglitsch, P., F. Schram. 1991. Invertebrate Zoology, Third Edition. New York, NY: Oxford University Press, Inc.
Oesch, R. 1984. Missouri naiades, a guide to the mussels of Missouri. Jefferson City, Missouri: Missouri Department of Conservation.
Szymanski, J. 1998. Leptodea leptodon (scaleshell mussel) rangewide status assessment. Fort Snelling, Minnesota: U. S. Fish and Wildlife Service. Accessed October 10, 2005 at http://library.fws.gov/Pubs3/statusass/scaleshellmussel.pdf.
Watters, G. 1995. A guide to the freshwater mussels of Ohio. Columbus, Ohio: Ohio Department of Natural Resources.
van der Schalie, H. 1938. The naiad fauna of the Huron River, in southeastern Michigan. Miscellaneous Publications of the Museum of Zoology, University of Michigan, 40: 1-83.