Chroomonas monococca is a species of cryptophyte alga in the family Chroomonadaceae, found in freshwater and potentially brackish aquatic environments in Europe. The specific epithet monococca, derived from the Greek for single grain, may refer to a distinctive unicellular morphology or the simple, solitary occurrence of cells without colonial aggregation. Cryptophytes in the genus Chroomonas are typically solitary, motile flagellates, so this epithet may emphasize a particular cell shape characteristic. Chroomonas species contain a characteristic plastid of secondary red algal origin, with a retained nucleomorph and a pigment complement including chlorophyll a, chlorophyll c, beta-carotene, and one of several phycobiliproteins depending on the species. These photosynthetic pigments collectively enable efficient absorption of light across a broad spectrum, contributing to the ecological success of cryptophytes across a range of light environments. Chroomonas monococca inhabits freshwater phytoplankton and periphyton communities and contributes to primary production in its aquatic habitat. It has been recorded from European freshwater localities and is one of numerous described species in this taxonomically diverse genus. Conservation status has not been assessed by the IUCN.