Summary ³

The pyramid pigtoe, scientific name Pleurobema rubrum, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.

Diagnostic description ⁴

Pleurobema plenum, Pleurobema cordatum, and Pleurobema sintoxia (= Coccineum) may be found with Pleurobema rubrum and are difficult to distinguish to the untrained eye. P. rubrum is the most prosogyre of the group, has the umbos situated the furthest forward, and often has pink nacre within the shell. The shell of this species may also be confused with large river ecophenotypes of Fusconaia flava (undata form) but differs in having a shallower beak cavity and in having the teeth set against the anterior margin without an intervening shelf (Stansbery, pers. comm.). Nevertheless, it is suggested that specimens be positively identified by a professional before any other actions are undertaken.

Distribution ⁵

Global Range: (5000-20,000 square km (about 2000-8000 square miles)) Historically this species was distributed throughout the Mississippi, Wabash, Tennessee, and Ohio River systems. It appears to never have been common, consisting of less than 4% of those species found in prehistoric middens (Parmalee, 1967; Klippel and Bogan, 1980). Today the species is widely but very sporadically distributed. It has apparently been extirpated from much of its former range. Shimek (1921) reported it from the Mississippi River at Prairie du Chien, Wisconsin, but it has not been recovered since that time (Havlik and Stansbery, 1977), although Havlik (1983) reported dead shells in the Mississippi River Pool 8 in Wisconsin. Starrett (1971) did not find this species in a survey in 1966 of the Illinois River although it was known to occur there prior to 1900. It was found in the Tuscarawas River of the Muskingum River in Ohio by Hildreth (1828, as Unio undatus Variety B), Dean (1890), Sterki (1894, 1900), and Ortmann (1919) but has not been recently collected there. Williams (1969) and Dames and Moore (1980) recorded it from the Ohio River, in the vicinity of Clermont County, Ohio, but an extensive survey in 1984 did not recover it (Stansbery and Cooney, 1985). It has been extirpated from the Tennessee River in Alabama (Stansbery, 1976). It has been extirpated from the Wabash and East Fork White rivers in Indiana, the Osage River in Missouri, the Beech Fork Salt and Licking Rivers in Kentucky, and the Stones and Holston Rivers in Tennessee. A few small populations in Big Black and Yazoo River drainages on Mississippi (Jones et al., 2005). The species is fairly widespread and can be locally common in Arkansas (often as Pleurobema pyramidatum, with which it has been synonymized- see Johnson and Baker, 1973) in areas such as the Little Missouri, Saline, and Ouachita Rivers (Harris et al., 1997). In Louisiana, Vidrine (1993) listed it (as Pleurobema pyramidatum) from Bayou Bartholomew, the upper Mississippi River, Tensas River, Boeuf River, Ouachita River, and Bayou Dorcheat; all in northern Louisiana into Arkansas.

Habitat ⁶

Habitat Type: Freshwater

Comments: This mussel typically inhabits large rivers but may occur in medium-sized lotic environments. It tends to occupy riffles or shoals in relatively shallow water and coarse-particle substrates, along sand bars, or in deep water (>4 m) with stable mud and muddy sand bottoms (Watters et al., 2009). Moderate to swift currents usually are associated with these habitats (Gordon and Layzer, 1989). It persists below some Tennessee River dams in sub-lotic zones of the next reservoir which have substantial currents from power releases.

Iucn red list assessment ⁷

• Needs updating

Assessor/s

• 1994
  Indeterminate (I)
• 1990
  Indeterminate (I)
• 1988
  Indeterminate (I)
• 1986
  Indeterminate (I)

Nature serve conservation status ⁸

Rounded Global Status Rank: G2 - Imperiled

Reasons: This species has experienced some decline and habitat loss although several populations remain, some with significant numbers especially in Arkansas and possibly northern Louisiana. Range is still wide but declines continue and the species is threatened by habitat degradation.

Intrinsic Vulnerability: Unknown

Comments: Sensitive to pollution, siltation, habitat perturbation, inundation and loss of glochidial hosts.

Environmental Specificity: Unknown

Sources and Credits

1. Rafinesque, 1820, no known copyright restrictions (public domain), http://commons.wikimedia.org/wiki/File:Naturalis_Biodiversity_Center_-_ZMA.MOLL.418472_-_Pleurobema_rubrum_(Rafinesque,_1820)_-_Unionidae_-_Mollusc_shell.jpeg
2. (c) rkkessler, all rights reserved
3. Adapted by rkkessler from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Pleurobema_rubrum
4. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28870296
5. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28870291
6. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28870300
7. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/34659761
8. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28870284

More Info

• iNat taxon page
• Animal Diversity Web
• Biodiversity Heritage Library
• BOLD Systems BIN search
• Global Biodiversity Information Facility (GBIF)
• NatureServe Explorer 2.0
• SeaLifeBase
• World Register of Marine Species

Range Map

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