Desmid of the month
Just like in Cosmocladium constrictum interconnecting cell strands in the colonial desmid C.
perissum are hardly detectable. In addition, colonies in this species
usually number but a few cells rendering distinction from given Cosmarium species even more problematic. Only highly incidentally large colonies are met
with in which the Cosmocladium-specific arrangement of cells is clear.
Actually, only in September 2007 the occurrence of C. perissum in the
Netherlands was established beyond any doubt when well developed colonies were
encountered in samples from a mesotrophic peat pit.
Colony of Cosmocladium perissum. The Cosmarium-like cells, characterized by a rather shallow, open, obtuse-angled sinus, are arranged in series showing both frontal, lateral and apical cell view.
The same colony but now in higher contrast
showing delicate, interconnecting cell strands.
Cell dimensions (L x B): 13 x 13 µm
Images Jan Šťastný, © RIZA/Waterdienst (mouse over)