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WESTERN RIDGE MUSSEL
Gonidea angulata
Family Unionidae - Pearly Mussels
Order Eulamellibranchia - Clams and Mussels
Risk Status
Official status
Freshwater molluscs are not included in a list of rare and threatened terrestrial
and freshwater invertebrates of British Columbia because little is known
of their distribution and status. Though elsewhere in North America they
are among the most vulnerable of invertebrate
groups to environmental degradation.
Image Credits: Western Ridge Mussel sketch
in 'Rare Invertebrates of the South Okanagan' by Hannah Nadel
image from: Fresh Water Molluscs
of Canada,
Arthur H. Clarke. Courtesy of the Canadian
Museum of Nature, Ottawa, Canada.
Distinguishing
features
Another common name for the Western Ridge Mussel is the Rocky Mountain
Ridged Mussel.
The shell of the Western Ridge Mussel is up to 125 mm long, 65 mm high,
40 mm wide, and with a shell wall up to about 5 mm thick at mid-anterior.
They are variable in form but typically rather thin, trapezoidal in shape.
They are yellowish brown to blackish brown on the outside and centrally
white or salmon to pale blue on the inside of the shell.
The beak sculpture is
compose of about 8 rather coarse, concentric ridges that are straight
in the centre and curved at both ends. The hinge teeth are irregular and
poorly developed.
Distribution
Map
Red dots indicate museum specimen records or confirmed breeding sites.
British Columbia
The Western Ridge Mussel has been found in the Columbia River system in
southern British Columbia (Okanagan and Kootenay rivers). This freshwater
mussel is known in Canada only from the main, valley bottom water bodies
from Penticton south. There have been few searches for it, and the only
recent records are from the Okanagan River at Okanagan Falls, Vaseux Lake
and Osoyoos Lake.
North America
The Western Ridge Mussel is found south in the Pacific drainage to southern
California.
Habitat
In Vaseux Lake near Oliver, British Columbia, large specimens of the
Western Ridge Mussel occur in muddy sand at a depth of 0.6 to 0.9 m along
the shoreline edge of a bed of pond weed. Elsewhere it occurs in rivers
and lakes and on various substrates. Four specimens were collected on
6 August 1972 from Vaseux Lake, and none were gravid.
Why is it endangered?
Rare invertebrates of the south Okanagan and Similkameen valleys such
as this species are threatened not by direct exploitation, but by loss
or degradation of their habitats. They are at risk because their ecosystems
are at risk.
The massive diversity of invertebrate species in British Columbia makes
it very difficult for entomologists to do a literature or collection survey
to determine which species are endangered or threatened. Specialized,
detailed surveys will be required for almost every species that is suspected
of being endangered. Despite a general ignorance about invertebrate distribution,
information is known about a number of species that are confined to threatened
habitats of very limited extent in the Thompson-Okanagan valleys.
The unionid mussels - the family that the western ridge mussel belongs
to - are very sensitive to environmental changes and consequently have
a high percentage of endangered species within their ranks throughout
North America.
Biology
Members of the Unionidae family are characterized by a short breeding
season.
Sources for more information
Related On-line Sites to Visit
Publications
Biodiversity of BC, Cannings, Ch4. , 1994, p. 48.
Rare Invertebrates of the South Okanagan, brochure, MOE, March 1995
Clarke, A.H. The Freshwater Mussels of Canada. National Museums of
Canada. Ottawa, 1981.
Museum Specimens
this section sponsored by:
Industry Canada
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