Morphological study of the coenobium of Coronastrum lunatum (Chlorophyceae)

Coenobia of Coronastrum lunatum, collected from a shallow, hypertrophic lake in Japan, were re-examined by light and scanning electron microscopy. Each cell contained a single parietal chloroplast, with a single pyrenoid surrounded by a starch sheath. Cells were lunate or triangular in side view and surrounded by a thin mucilage wall. A slightly curved (awl-shaped) lower appendage on the cell wall was 1-1.5 times the length of the cell itself, but the upper appendage was smaller or not distinctive. Adjacent cells of a coenobium were connected by a short and colourless pad, which was attached medially on the long axis of the cell. The quadrate arrangement of coenobia on a flat plate, a large pyrenoid, asynchronous division of the coenobium, and lower appendages connected with a thin mucilage wall without a septum are newly characterized. Differentiation from similar genera of coenobial green algae are discussed.