Eunotia perpusilla

Valves are dorsiventral. The ventral margin is concave, with two subapical swellings. The dorsal margin is convex and undulate, with the number of undulations varying with valve size (typically 3-4). Striae are radiate, evenly spaced, with occasional shortened striae intruding from the dorsal margin. Apices are protracted, capitate, and weakly recurved. Terminal raphe ends are distinct in LM and positioned near the ventral margin.

Additional nomenclatural observations

In Van Heurck’s Atlas (1880-1881), a drawing with the caption “E. tridentula Ehr. var.? perpusilla Grun.” was published. In the “Table Alphabetique” (the accompanying text for the Atlas plates), which was published in 1884, Van Heurck changes his mind and drops the “var.? perpusilla”, leaving “E. tridentula Ehr.” and still referring to the same figure in the Atlas (Pl. XXXIV, Fig. 31).

In 1939, A. Berg elevated E. tridentula var. perpusilla to the rank of species, resulting in Eunotia perpusilla (Grunow) Berg. While he did not specifically include the text “stat. nov.”, at the time this was not required of him and the omission does not invalidate his transfer.

It is the author’s opinion that E. muscicola var. tridentula Nörpel and Lange-Bert. 1993 (and its current form Eunotia paratridentula Lange-Bert. and Kulikovsky 2011) is conspecific with E. perpusilla (Grunow) Berg, as illustrated in Van Heurck’s Atlas.

It should be noted that Lange-Bertalot has a separate interpretation of the identity of E. perpusilla. He believes that E. perpusilla (referring to its basionym E. tridentula var. perpusilla) is synonymous with E. microcephala Krasske ex Hustedt 1932, and we believe this to be incorrect (Lange-Bertalot et al. 2011). Lange-Bertalot and Nörpel also considered Eunotia perpusilla Grunow sensu Patrick 1958 to be conspecific with E. muscicola var. tridentula (Krammer and Lange-Bertalot 1991). Lastly, it should also be noted that Patrick referred to North American specimens, such a those above, as E. perpusilla. Unfortunately, she attributed the incorrect authority, using Grunow, instead of (Grunow) Berg (Patrick 1958).