Cell of Penium exiguum marked by capitate apices.
Cell dimensions (L x B): ca 50 x 10 µm
Like P. margaritaceum P. exiguum is marked by a finely granulate cell wall. As compared to P. margaritaceum, P. exiguum is smaller in size but more distinctive are the subapical constrictions resulting in capitate cell ends. Girdle bands (which are characteristic of the genus Penium) usually are well to be distinguished. In the Netherlands P. exiguum is occasionally encountered in acidic, oligo-mesotrophic moorland pools. Zygospores, as in other Penium species globose and smooth-walled, are only incidentally found.
Another cell of P. exiguum. Notice the finely granulate cell wall and the occurrence of girdle bands.