Nephrocytium is a genus of green algae in the class Chlorophyceae.

[1] Nephrocytium consists of colonies of 4, 8, or 16 asymmetrical cells surrounded by a spherical to ovoid layer of mucilage, which is formed when the mother cell wall expands and gelatinizes.

It exclusively forms autospores, and does not appear to have a flagellated stage in its life cycle.

[1] Similar genera include Nephrochlamys and Juranyiella; Nephrochlamys differs in having cells that lack pyrenoids, while Juranyiella has granules dotted on the cell wall surface.

However, cells enlarge during their life cycle, which must be taken into account while identifying Nephrocytium species.