Pisidium moitessierianum

Pisidium moitessierianum is a species of minute freshwater clam. It is an aquatic bivalve mollusc in the family Sphaeriidae.

Description
This species is the smallest of the pea clams or Pisidium species, and the smallest of any freshwater bivalve, at 1.5 – 2.5 mm adult size. The shell is long-oval and oblique wedge-shaped with prominent umbos which are slightly behind the midpoint. The umbos are demarcated by a shallow furrow. The surface (periostracum) is silky, with regular concentric striae.

Distribution
The species is native to Europe but has been introduced to northeastern North America.
 * Czech Republic – in Bohemia, in Moravia, - endangered (EN)
 * Slovakia
 * Germany – endangered (gefährdet)
 * Nordic countries: Denmark, Finland, Norway and Sweden (not in Faroes, Iceland)
 * Great Britain and Ireland