Micrasterias is a Desmid - a group of green algae mostly found in neutral to acidic fresh waters and sphagnum bogs. Most are unicellular, though a few form chain-like colonies. Each cell is constructed of 2 semicells which are mirror images of each other. In Micrasterias the cells are flattened and the margins of the semicells highly ornimented. The nucleus is central.
Credit: Wellcome Images