Septum

A septum is a silica sheet extending internally from the walls of a copula, or girdle band, occluding a portion of its length. By contrast, a septum is part of a copula, while a pseudoseptum is part of a valve. The plural is septa. Septa are found in genera such as Tabellaria.

Citations

Koppen, J.D. (1975) A morphological and taxonomic consideration of Tabellaria (Bacillariophyceae) from the northcentral United States Journal of Phycology 11: 236-244
Round, F.E., Crawford, R.M. and Mann, D.G. (1990) The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.

Septae3 — In this SEM micrograph, septa of *Tabellaria* are marked with arrows. Each septum is attached to a girdle band, or copula. A valve of *Tabellaria* (internal view) lies between the two copulae.