Guide to Actinella

Cells of Actinella grow singly, or in small colonies that are joined by mucilage secreted at the narrow ends of the cells. Valves are distinctly asymmetric to the apical and transapical axes. The raphe is highly reduced and is restricted to the ventral margins of valves. Helictoglossae are distinct as dark, silicious thickenings on the ventral margins. Small to large spines are present on the valve margins.

The species Actinella punctata is the only taxon known from North America. Nearly all records of A. punctata are from acid waters in eastern and southeastern US states. Actinella is differentiated from Eunotia by asymmetry about the transapical axis. A large number of species are known from South America and Australasia.