Cell shape is ovoid to pyriform, asymmetric, more or less flattened. A more or less pronounced flagellar groove may be present.
Cell surface is apparently smooth, but may bear extrusomes, the subsurface layer often with trichocysts.
Swims by rapid movements of the anterior-pointing flagellum that pull the cell, the posterior-pointing flagellum is apparently less active.
Marine species are yellow to yellowish-brown.
Chloroplasts are many and discoid with thylakoids in triplets and +/- girdle lamellae
Pyrenoids are naked, submerged, and on the iside of chloroplasts.
Only phototrophic species are presently known.