Guide to Crenotia

SPECIES OF CRENOTIA ARE NOT KNOWN TO OCCUR IN NORTH AMERICA (YET)

The frustules of Crenotia are heterovalvar, with slightly to strongly concave raphe valve (hypovalve) and convex rapheless valve (epivalve). The valves are lanceolate, linear-lanceolate, elliptic-lanceolate and the small cells are elliptic. Some species have a gibbous center. The apices are rounded, (sub)rostrate or capitate. Striae are uniseriate to biseriate, zig-zag arranged, and radiate throughout both valves. The raphe is filiform with long terminal raphe fissures curved unilaterally around the densely arranged terminal striae (the effect of truncated valve apices in the LM).

Many Crenotia species have an asymmetric central area on the rapheless valve. A rimmed depression may be present on the inner side of the central part of the valves (visible in the LM as a shadow, in German 'Fleck'). In girdle view, the valves are slightly to markedly bent around the median plane (a 'saddle' shape, double image effect in the LM). Cells may be free-living, attached to the substrate by a mucilaginous stalk, or in ribbon-like (band-shaped) colonies.

The genus Crenotia was established by A.Z. Wojtal (2013) based on unique morphological characteristics. Previously, the representatives were classified in the genera Achnanthidium Kütz. or Achnanthes Bory.

This genus includes only freshwater taxa. The name Crenotia refers to its common occurrence in thermal and mineral spring waters, but some species are also known from rivers, gravel pits, reservoirs, and creeks.