Coelastrum

About

Coelastrum is a genus of green algae in the Scenedesmaceae family. It is a common component of the phytoplankton in freshwater habitats such as ponds, lakes, waterfalls, and temporary pools of water, particularly eutrophic ones. The genus has a more or less cosmopolitan distribution, although some species appear to have more restricted geographical distributions. The name comes from the Greek terms koilos, meaning hollow, and astron, meaning star.

Summary from Wikipedia