Cosmarium excavatum
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images © Marien van Westen
(after material from English Lake District)

Cosmarium excavatum var. duplo-majus. Notice globose, granulate semicells mutually separated by an elongate isthmus.

Cell dimensions (L x B): 42 x 25 µm

mouse over images © Alfred van Geest (after Canadian material)

C. excavatum var. duplo-majus in vertical view. Notice circular outline of semicell and isthmus.



Desmid of the month
May 2022

Cosmarium excavatum

C. excavatum, a medium-sized granulate Cosmarium, is marked by an elongate isthmus and almost globose semicells. Cell wall granules are relatively large and evenly distributed over the wall (but lacking at the isthmus). From the Netherlands only C. excavatum var. duplo-majus is known, being almost twice as large as the nominate variety and found in one single moorland pool, in 1926.

Another cell of C. excavatum var. duplo-majus in frontal view (focussed on cell outline).




SEM picture of C. excavatum var. duplo-majus. Notice large, evenly distributed granules (each surrounded by a hexagon of pores)