Scaleshell
Leptodea leptodon
Summary 2
The scale shell or scaleshell (Leptodea leptodon) is a species of freshwater mussel in the family Unionidae, the river mussels. This aquatic bivalve mollusk has disappeared from much of its historical range. It is endemic to the United States, where it is now present in four or fewer states; it is only found with any regularity in Missouri. It is a federally listed endangered species of the United States.
Distribution 3
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 )
Ecology 4
No specific studies have examined the ecology of this species. Oesch (1984) notes that it requires quite clear, unpolluted water, indicating a rather low tolerance to disterbance. Its adaptations to withstand the physical forces inherent to riffles resemble those of Hemistena lata (shell completely burried in a vertical position with the foot extended as an anchor) (Gordon and Layzer 1989).
Habitat 5
Habitat Type: Freshwater
Comments: This species occurs in riffles with moderate to high gradients in creeks to large rivers. It is typically associated with riffles, relatively strong currents, and substrate of mud, sand , or assemblages of gravel, cobble, and boulder. It has been found completely buried in the substrate down to depths of 15 cm (Oesch, 1984; 1995). It occurs in medium to large rivers with low to moderate gradients in a variety of stream habitats including gravel, cobble, boulders, and occasionally mud or sand substrates (Buchanan, 1980; 1994; Oesch, 1995). Although always somewhat rare, this species historically was not habitat limited and once occupied a wide variety of habitats including riffle areas with assemblages of gravel, cobble, boulder, and occasionally mud or sand; as well as big rivers with muddy bottoms (Szymanski, 1998). Currently it is more restricted to rivers with relatively good water quality (Oesch, 1995) in stretches with stable channels (Buchanan, 1980).
Iucn red list assessment 6
Red List Category
Red List Criteria
Version
Year Assessed
- Needs updating
Assessor/s
Reviewer/s
Contributor/s
History
-
1994Indeterminate (I)
-
1990Indeterminate (I)
-
1988Indeterminate (I)
Morphology 7
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
Sources and Credits
- (c) rkkessler, all rights reserved
- Adapted by rkkessler from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Leptodea_leptodon
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31401844
- (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28882814
- (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28882816
- (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/34536758
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31401846
