A new freshwater species of the Cryptophyceae (Cryptomonas undulata) i
s described on the basis of observations of cell morphology, phycobili
protein pigment, habitat and behaviour in unialgal culture. The new sp
ecies has a peculiar, undulate cell shape. It possesses one bilobed ch
loroplast containing phycoerythrin III (566 nm). It can be distinguish
ed from related species by its characteristic cell morphology and its
special habitat - the region of the oxic/anoxic boundary layer.