Eunotia exigua

Frustules are narrow rectangles in girdle view. Ventral margin is concave. In smaller specimens the ventral margin is slightly concave or straight. Dorsal margin is convex. Apices are protracted, and frequently strongly dorsally reflexed. Apices of shorter specimens are more obtusely rounded. Helictoglossae are positioned close to the apices. Distal raphe end curves a short distance on to the valve face.

There is some variability in valve morphology of E. exigua between populations. For example, some populations are less silicified than others or the ventral margin is less convex. (compare first two specimens with last four specimens). Lange-Bertalot et al (2011) report broader specimens from Europe (3 to 4 µm) though earlier Krammer and Lange-Bertalot (1991) include narrower specimens (2 ?) 2.5 to 4 (5) µm. Patrick and Reimer (1966) report a range in valve width of 2 to 4 µm.

See further discussion around E. exigua taxonomy in Lange-Bertalot et al. (2011). Eunotia exigua sensu lato, a complex of closely related taxa, has recently had several taxa removed, such as E. cataractarum, E. orthohedra, E. exigua var. tridentula, E. exigua var. undulata, E. kruegeri, and others. Both habitat and a careful examination of valve outline and morphological characteristics will help distinguish taxa. More taxonomic work is needed.