Craticula Guide
Credit: Lauren Fuelling, Pat Kociolek, Sarah Spaulding
  1. Striae parallel, or nearly parallel
  2. Valves lanceolate
  3. Central area small or absent
  4. Distinct internal valves may be present

The valves of Craticula are lanceolate. The striae are distinctly parallel, or nearly parallel. The central area is greatly reduced or absent. The genus is polymorphic, forming different valve morphologies. There are three valve types found for this taxon: vegetative, heribaudii, and craticula forms. The three forms are produced as a cellular strategy for surviving desiccation (Schmid 1979). Two craticula are formed within the vegetative frustule. Subsequently the heribaudii cell is formed within the craticula. The heribaudii cell usually has different ornamentation compared to the vegetative cell. Note that these stages are not always present in a population, and for many of the smaller species, the craticular and heribaudii stages have not been observed. Living cells possess two elongate, plate-like chloroplasts appressed to the girdle.

Craticula is a term applied to internal valves that are formed within frustules that are normal in morphology. The craticular valves consist of a raphe-sternum and robust transverse bars. The genus Craticula occurs in epipelic habitats across North America, in fresh to brackish waters.