Cells ranges from spherical to ellipsoidal and can be either solitary or clustered in colonies. These colonies can contain up to 128 cells, occasionally reaching 256, and are typically polyhedral or pyramidal in shape. Most species of Micractinium produce long, narrow bristles that taper from base to tip. Each cell contains a single cup-shaped chloroplast with a single pyrenoid.Traditionally, Micractinium belenophorum has been distinguished from Chlorella by its tendency to form colonies and bristles. However, the species sometimes lacks these features, as they seem to be an inducible defense mechanism against grazers like rotifers.