Individual species have characteristic shapes and size ranges within these limits. A single nucleus is present, usually just beneath the basal bodies. Most of the cell volume is occupied by one or more grass-green chloroplasts. In the most familiar species, one cup-shaped chloroplast is present, but in other species the chloroplast may be reticulate, stellate or any of a variety of other shapes. Cell structure in these colonies, except for the absence of flagella, differs little from free-swimming cells.
Cysts are generally spherical and have thick walls with or without extensive surface ornamentation.
Cysts commonly are reddish due to the accumulation of secondary carotenoids and low chlorophyll content.