Image © Alfred van Geest
Cosmarium margaritiferum. Notice trapeziform semicells with truncate apex and slightly convex lateral sides.
Cell dimensions (L x B): 54 x 47 µm
C. margaritiferum is a medium- to rather large-sized species in the group of granulate Cosmaria. Semicells are trapeziform in outline with a truncate apex and slightly convex lateral sides. Cell wall granules are fairly coarse, evenly distributed and surrounded by marked pore fields (paricularly to be observed in the semicell centre). Zygospores are globose with broadly rounded, low-conical protuberances. In the Netherlands, C. margaritiferum is of occasional occurrence in mesotrophic pools and fen hollows. Zygospores are found a few times.
Cell of C. margaritiferum showing coarse, rather evenly distributed cell wall granules.
Image © Matthijs Koek
Zygospore of C. margaritiferum marked by broadly rounded, conical protuberances. Notice also marked cell wall pores in the centre of one of the empty gametangum semicells.