COSEWIC assessment and status report on the Rocky mountain ridged mussel Gonidea angulata in Canada
- Assessment Summary
- Executive Summary
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Literature Cited
- Biographical Summary of the Report Writers
- Authorities Consulted
- Collections Examined
Name and classification
|Species Name||Gonidea angulata (Lea, 1839) according to Clarke (1981): 1838 according to Taylor (1981) and Turgeon et al. (1998).|
|Family||Unionidae (Pearly Mussels) (higher classification from Turgeon et al., 1998)|
|Subfamily||Ambleminae according to Clarke (1981): Gonideinae according to Heard and Gluckert (1971) and Davis et al. (1978): tribe Gonideini according to Davis and Fuller (1981). Lydeard et al. (1996) consider the genus Gonidea as not closely related to any other North American forms. See discussion of ancestry and relationships below.|
|COSEWIC name:||Rocky Mountain Ridged Mussel|
Invalid usages include:
|Type Locality:||Taylor (1981) indicates that “Lewis’s River”, now interpreted as the Snake River, Idaho (with no specific locality), as the type locality for Gonidea angulata|
|Collections of G. angulata exist in the following museums:|
Several smaller institutions have been reviewed for lots of this species by Frest (1985-1997).
Museums that contain Canadian records include:
The taxonomy and relationships of this form are somewhat problematic at present, despite considerable study. Many authors, including Ortmann (1910, 1916), have regarded Gonidea as exceptionally distinctive, belonging to its own subfamily or family, ranked closest to the Amblemidae or Ambleminae among North American Unionoida (e.g., Heard and Gluckert 1971; Davis et al. 1978; Davis and Fuller 1981). Some authors, such as Heard (1974) and Taylor (1985, 1988), stress that it has possible Asian affinities. The first, rather preliminary, rRNA study of unionoideans placed Gonidea close to Ambleminae (Rosenberg et al., 1994). The more complete study by Lydeard et al. (1996) concluded that Gonidea is not closely related to any other North American Unionacea. Nagel et al. (1998) suggest relationship of the problematic European form Potamida littoralis to the Gonideini, based primarily on anatomical features. Unless Taylor (1988) is correct about the Korean unionid of Yoo and Habe (1962), there is only one extant taxon (without subspecies) and four fossil taxa (Watters, 2001). The most recent study, by Graf (2002), confirms the placement of Gonidea in the Ambleminae and recognizes that subfamily as endemic to North America.
Gonidea angulata is a large freshwater mussel that exhibits features typical of its subfamily Ambleminae (Elliptioninae). The subfamily Ambleminae is characterized by heavy hinge teeth; however, G. angulata has a moderately heavy hinge but rather indistinct hinge teeth. The Ableminae is also characterized by all four demibranchs being marsupial, by hookless glochidia, and by a short breeding season (tachytictic).
Clarke (1981) provides the following description for G. angulata: “Shell up to 125 mm long, 65 mm high, 40 mm wide, and with shell wall up to about 5 mm thick at mid-anterior; variable in form but typically rather thin, trapezoidal in shape, with posterior margin obliquely flattened and relatively broad, and with a sharp and prominent posterior ridge running from the umbo to the angular basal posterior margin of each valve (Figure 1). Shell with obscure radial sculpturing on the posterior slope and readily apparent growth rests. Periostracum yellowish brown to blackish brown, without rays, smooth on the disc, and roughened on the posterior slope. Nacre centrally white or salmon, but pale blue posteriorly and near the margin. Beak sculpture composed of about 8 rather coarse, concentric ridges that are straight in the centre and curved at both ends. Hinge teeth irregular and poorly developed; pseudocardinal teeth compressed, low, laterally expanded, 1 in the right valve and none or 1 in the left; lateral teeth absent.”
Frest and Johannes (in press) add: “See Burch (1973, 1975) for best short description and illustration (1973, figure 11). This taxon is very distinctive. Gonideaangulata has a moderately heavy hinge but rather indistinct hinge teeth; has a sharp posterior ridge; the posterior length exceeds the anterior, but the shell is not winged; shell periostracum generally greenish, sometimes lightly rayed with yellow; shell generally thin; nacre coppery blue-white; length 7-more than 9 cm.” ( Figure 2).
Figure 1. Image of Gonidea angulata showing the angular ridge typical of this species.
Figure 2. Drawing of Gonidea angulata (from Burch 1975).
For another illustration, see McMahon and Bogan (2001, fig. 28U).
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