Pleurobema riddellii

Louisiana Pigtoe

FWS Focus


The Louisiana pigtoe is a rare freshwater mussel with a thick, inflated, triangular to sub-quadrate shell. The beaks are elevated well above the hinge line but are sometimes eroded. The external shell is without sculpturing and reddish-brown, dark brown, or black in color. The interior shell surface (nacre) is typically white, rarely peach tinted, and iridescent posteriorly. Pseudocardinal teeth (molar-like structures located near the beaks on the interior surface) are heavy to massive, triangular and rough with the anterior tooth in the left valve compressed and parallel to the margin. The lateral teeth, two in the left valve and one with a basal flange in the right, are short and straight or slightly curved. Soft tissues are described as white to off-white. Individuals approaching 5 inches (127 mm) in length have been collected in Texas. The Louisiana Pigtoe is a medium-sized freshwater mussel (shell lengths to greater than 62 mm) with a brown to black, triangular to subquadrate shell without external sculpturing, sometimes with greenish rays. Burlakova et al. (2011a, p. 158) considered the species rare throughout its range. Other native mussel species (e.g. Pimpleback, Cyclonaias pustulosa; Texas Pigtoe, Fusconaia askewi; Trinity Pigtoe, F. chunii; and Wabash Pigtoe, F. flava) can easily be mistaken for Louisiana Pigtoe when identified by shell morphology alone. A recent survey suggested experienced malacologists had a 76% success rate accurately identifying the species in the Little River, Oklahoma, when field identifications were compared with genetic analysis results (Inoue 2018,p. 1).

Scientific Name

Pleurobema riddellii
Common Name
Louisiana pigtoe
FWS Category

Location in Taxonomic Tree

Identification Numbers



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