Cosmarium sphyrelatum. Notice semicells consisting of a more or less rectangular basal part and a  smaller, likewise rectangular apical part. Apex with a faint median indentation.

Cell dimensions (L x B): 18 x 13 µm



Desmid of the month
October 2019

Cosmarium sphyrelatum

C. sphyrelatum is a but little known species belonging to the large group of small-sized, smooth-walled Cosmaria that can readily be confused with each other. Semicells of  C. sphyrelatum consist of a more or less rectangular basal part and a smaller, likewise rectangular apical part whereas the apex itself is marked by a slight indentation. C. sphyrelatum much resembles given forms of C. regnellii and C. trilobulatum. Main characteristic distinguishing it from those species is its strongly scrobiculate cell wall, often with an extra large pit in the midregion of the semicell, usually combined with a local unsculptured inflation (Coesel 1989). In the Netherlands, C. sphyrelatum is of occasional occurrence in shallow, slightly acidic, mesotrophic water bodies, in particular quaking fen hollows.

Coesel, P.F.M., 1989. Taxonomic notes on Dutch desmids. Cryptogamie, Algologie 10: 181-193.

Image © Marien van Westen

Empty cell of C. sphyrelatum showing in each semicell a large central cell wall pit .

Image: Hanny Kooijman née Van Blokland © IBED

SEM picture of C. sphyrelatum showing a markedly scrobiculate cell wall with a large central pit in each semicell.

SEM picture of another cell of C. sphyrelatum in which the upper semicell shows a central pit combined with an unsculptured inflation and a lower semicell in which the central pit is wanting.