Fawnsfoot (Truncilla donaciformis) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:
Truncilla donaciformis (Lea, 1828)
English common name:
Fawnsfoot
French common name:
Troncille pied-de-faon

The recognized authority for the classification of aquatic molluscs in Canada is Turgeon et al. (1998). The currently accepted classification for this species is:

Kingdom:
Animalia
Phylum:
Mollusca
Class:
Bivalvia
Subclass:
Paleoheterodonta
Order:
Unionoida
Superfamily:
Unionoidea
Family:
Unionidae
Subfamily:
Lampsilinae
Genus:
Truncilla
Species:
Truncilla donaciformis

Morphological description

The following description is modified from Metcalfe-Smith et al. (2005a), Cicerello and Schuster (2003), Parmalee and Bogan (1998) and Clarke (1981). The Fawnsfoot (Figure 1) is a small freshwater mussel with a typical adult length in Ontario of approximately 35 mm and a reported maximum length of 45 mm. The shell is moderately thick, oval to triangular, rounded on the anterior end and bluntly pointed on the posterior. The prominent posterior ridge is rounded and flattened dorsally. The beaks are full, central and slightly elevated above the hinge line. Beak sculpture consists of 3-8 fine bars; the first is concentric while the others are weakly double-looped. The shell is smooth, yellow to greenish with numerous dark green rays often broken into v-shaped or chevron markings. The hinge teeth are fully developed with two thin, compressed, divergent, serrated pseudocardinal teeth in the left valve. The posterior tooth is located directly below the beak and flared upward. The right valve has one flattened, triangular pseudocardinal tooth. The lateral teeth (two in the left valve, one in the right) are thin, straight and long. The Fawnsfoot is easily distinguished from all other Canadian species of freshwater mussels by the large chevron-shaped markings on its shell coupled with its very small size. The Deertoe, Truncilla truncata, may also have chevron-shaped markings on its shell but they are finer. The Deertoe also grows about twice as large as the Fawnsfoot and has a sharply angled, rather than rounded, posterior ridge.

Figure 1. Live specimens of the Fawnsfoot (Truncilla donaciformis) collected from the Grand Riverin 1997. Photo courtesy of the National Water Research Institute.

Figure 1. Live specimens of the Fawnsfoot (Truncilla donaciformis) collected from the Grand Riverin 1997. Photo courtesy of the National Water Research Institute.

Genetic description

There is no information available on the genetic structure of North American populations of the Fawnsfoot. However, the remaining Canadian populations (see Canadian range) are isolated from one another by large distances (40 – 700 km), and Zanatta et al. (2007) have shown that genetic isolation in Canadian populations of freshwater mussels is possible over these spatial scales.

Designatable units

All Canadian populations are found within the Great Lakes-Upper St Lawrence National Freshwater Biogeographic Zone. There are no known distinctions among populations that warrant consideration for designation below the species level.

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