Cl. closterioides is one of the few Closterium species the cells of which are not curved (lunate) but perfectly straight. In this respect it may be compared with Cl. navicula but its cell dimensions are distinctly larger and, linked to that, chloroplasts contain 3-6 pyrenoids (versus 1-2 in Cl. navicula). Not seldom, the chloroplasts are transversely notched or even divided in two (or three) parts. In the Netherlands, Cl. closterioides is a rather rare species in acidic, oligotrophic bog pools.
Image © Marien van Westen
Another cell of Cl. closterioides. Notice partitioned chloroplasts.
Image © Koos Meesters
Cell of Cl. closterioides showing some 5 pyrenoids in each chloroplast.