Cyclostephanos Guide
Credit: Lena Iversson
  1. Striae fasciculate, extending from valve face to mantle
  2. Costae may form 2 branches on mantle
  3. Rimoportulae positioned near, and below spine on mantle

The striae of Cyclostephanos are organized into bundles, or fascicles, that extend from the valve face onto the mantle. The costae, or thickened ribs, also extend from the valve face to mantle. The costae branch on the valve mantle below the plane of the marginal spines, a key feature of the genus. Marginal rimoportulae are positioned near the spines, if spines are present. The branching costae distinguish this genus from Cyclotella and Stephanodiscus. Note that many of these features can seen only with SEM, particularly in the smaller species.

Although species within the genus are found in a variety of habitats, many are indicators of eutrophic conditions. In North America, smaller species of Cyclostephanos often dominate the plankton flora during spring and summer in nutrient rich lakes and rivers. Many of the species are tolerant of elevated levels of total dissolved solids and are present in highly calcareous or saline waters. Cyclostephanos is probably more common that currently reported in surveys because it has not been included in keys and references. The genus includes C. dubius, C. damasii, C. invisitatus, C. costatilimbus and C. tholiformis.

Note that Round’s (1982) description of the genus Cyclostephanos was invalid. Consequently, all of the taxa transferred to Cyclostephanos at that time were also invalid.