Annulus (Geissleria)

Annulus (centric taxa)



In the genus Geissleria, a circular or semi-circular hyaline area on the valve face which interrupts two or more distal striae. An annulus may be distinctive or barely discernible, depending on species. Plural form is annuli.

In Krammer et al. (2000) the definition is in the key for the Navicula group Annulatae. The species in this group have been elevated to the genus Geissleria.


Krammer, K. and Lange-Bertalot, H. (2000). Bacillariophyceae 5. English and French translation of the keys. In: Büdel, B., Gärtner, G., Krienitz, L. & Lokhorst, G. M. (eds.). Süßwasserflora von Mitteleuropa. 2(5), 311 pp. Spektrum Akademischer Verlag, Heidelberg-Berlin.