Cosmarium formosulumImage © Alfred van Geest

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.

Cosmarium formosulum, empty cell
Image © Marien van Westen

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.

Cosmarium formosulum, empty cell in lateral view
mouse over images © Alfred van Geest

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

Cosmarium formosulum, SEM image
Image © Marien van Westen

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