Cells pale green, spherroidal to ellipsoidal, sometimes having swollen protuberances. Cells occuring singly or weakly held together in irregular chains that may branch forming irregular colonies. Cell size ranging from 2.5 to 5.5 micrometers diam. Flagellate stages not present. Cells enclosed by a three layered cell wall having diffuse fibrillar material on the outer surface (possibly mucilage). Cultured cells adhere strongly to surface of glass container. Protoplasm consisting of a single, relatively large nucleus, a single chloroplast, one or possibly several mitochondria, a single dictyosome, endoplasmic reticulum and peripheral oblong bodies. Granular Polysaccharide reserve material not present. Chloroplast pigments are chlorophylls a, c diatoxanthin, diadinoxanthin, fucoxanthin like pigments, and carotene.