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Class Bivalvia

(Clams and mussels)

Soil & Water Conservation Society of Metro Halifax (SWCSMH)

Updated: October 09, 2013      Freshwater Benthic Ecology and Aquatic Entomology Homepage


Photograph: (clam)- Family: Corbiculidae


Contents:



Introduction

This group includes clams and mussels which typically occur in most freshwater habitats and may be particularly abundant in certain streams. Although the clams and mussels have a wide range of tolerances to pollution with some species being very sensitive to water quality, habitat and biological conditions, a number of species of this group (especially clams) can tolerate somewhat degraded conditions.

This group is distinguished by:

As a general rule, mussels are large and have a flat, more oblong shell shape, while freshwater clams are smaller (3/4 inch) and typically more round. In addition, freshwater clams are usually symmetrical with the umbo (the highest point on the shell) equally distant from both ends. Mussel shells are usually lopsided with the umbo closer to the end.

All freshwater clams are filter feeders, subsisting on phytoplankton, zooplankton, detritus, and bacteria. Some species of fish consume clams regularly, and several species of mammals, most notably muskrats and racoons prey heavily on unionaceans. The shells of unionaceans are used in the Japanese cultured-pearl industry.


Diagnostic features (Mackie, 1998)

[Img-bivalvia_id.jpg]



Indicator value

(Mackie, 2001)

There are two families of bivalves native to North America, the Sphaeriidae (fingernail clams) and the Unionidae (freshwater pearly mussels), and two families that were introduced from Europe, the Corbiculidae (Asian clams) and the Dreissenidae (zebra and quagga mussels). All bivalves are filter-feeding organisms.

This group includes clams and mussels which typically occur in most freshwater habitats and may be particularly abundant in certain streams. Although the clams and mussels have a wide range of tolerances to pollution with some species being very sensitive to water quality, habitat and biological conditions, a number of species of this group (especially clams) can tolerate somewhat degraded conditions (Peckarsky et al, 1990).

Mussels have larval stages that are parasitic on specific fish species and are dependent on this host fish species for dispersal within aquatic systems. As a result, problems such as barriers to fish movement, or the reactions of mussels or host fish species to environmental conditions may cause complex and variable responses in mussel populations. Because of their long life span and sensitivity to environmental change, most species of mussels are good indicators of water quality.

"Dead" clams or mussels (empty shells) do not accurately reflect water quality because shells can persist for long periods regardless of water conditions. The life is long, 1 to 15 years in clams, and productivity is relatively low (Kellogg, 1994).



References and web URLs:





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