Biremis Guide
Credit: Marina Potapova
  1. Valves with linear margins
  2. Striae not continuous across valve face
  3. Striae chambered, open externally in circular or slit-like foramina
  4. Valve mantle with similar chambered striae

Biremis currently contains both freshwater and marine species. Freshwater species possess a linear margin and bilateral symmetry, while marine species are strongly dorsiventral, with amphoroid symmetry. The striae of Biremis appear to be "interrupted" (they are not continuous), due to internal plates that cover marginal chambered striae. Internally, the striae are chambered, while externally they open in circular or slit-like foramina (SEM feature). The striae on the valve mantle are also chambered, with circular or slit-like foramina. Cells grow singly, rather than in colonies.

Biremis is found in sandy sediments of both marine and freshwater habitats. Although originally described from marine habitats (B. ambigua), Biremis also contains several freshwater taxa. Biremis zachariasii and B. undulata are found in deep oligotrophic lakes, while several endemic species are known from Tasmania. Some species now in Biremis were previously considered in Oestrupia and Caloneis.