Cell of Cosmarium pachydermum. Notice large dimensions, moderately deep constriction and relatively thick wall penetrated by distinct pores.
Cell dimensions (L x B): 93 x 74 µm
Cosmarium pachydermum is characterized by large, smooth-walled cells that are oblong-elliptic in outline with a moderately deep median constriction. Cell wall is rather thick and provided with distinct, densily set pores. In the Netherlands, C. pachydermum is a rather rare species in slightly acidic, mesotrophic habitats, in particular quaking fen hollows.
Image © Alfred van Geest
Cosmarium pachydermum var. aethiopicum, differing from the nominate variety by somewhat smaller, relatively broader cells with a thinner wall.