I found Dolichospermum planctonicum in August 2025 in the plankton of the Mühlhalden pond. The filaments of this cyanobacterium floated in a greenish layer on the water surface, mixed with other species of algae and cyanobacteria.

The characteristic features of Dolichospermum planctonicum are the ellipsoidal heterocysts and round akinetes, which are almost always separated from each other by several vegetative cells (s. figs 2 a-b and 3 a-b). Only rarely are directly adjacent pairs of akinetes or heterocysts can be found. The vegetative cells are spherical and have almost the same size as the akinetes. They contain gas vacuoles, which is why the trichomes often appear black at low magnifications. The cell walls of both the akinetes and the heterocysts are smooth without structure. The trichomes are surrounded by a clearly visible, gelatinous sheath that has a thickness of 10–20 µm (s. fig. 1).