Cosmarium formosulum. Notice pyramidal-trapeziform cell outline with bigranulate crenations.
Cell dimensions (L x B): 60 x 54 µm



Desmid of the month
June 2015

Cosmarium formosulum

C. formosulum is a granulate Cosmarium that can easily be confused with a number of roughly similar species. Semicells are pyramidal-trapeziform. Essentially in identification is the outline of the semicells, viz., faintly crenate, each of the crenations being marked by two granules.The supraisthmial region is slightly inflated and furnished with a number of longitudinal, more or less curved series of granules. Between this central ornamentation and a number of radiating series of granules towards the marginal crenations there is an unsculptured zone. In the Netherlands, Cosmarium formosulum is a common species in various kinds of meso-eutrophic water bodies, both slightly acidic and alkaline.

Empty cell of Cosmarium formosulum showing supristhmial inflation ornamented with a number of curved longitudinal series of granules . Notice also radiating series of (paired) granules towards the cell margin.

Empty cell of Cosmarium formosulum in lateral view better showing the supraisthmial inflation.

SEM picture of Cosmarium formosulum. Notice the unsculptured zone between central semicel ornamentation and radiating series towards the margin.