Chroomonas collegionis is a species of cryptophyte alga in the family Chroomonadaceae, documented from freshwater environments. The specific epithet collegionis may refer to a collegiate institution or academic collection where the type specimen was described or preserved. Chroomonas species are small, biflagellate, unicellular eukaryotes that possess a plastid of secondary red algal origin, with a retained nucleomorph that is unique among eukaryotic algae. The cells of Chroomonas are typically ovoid, compressed, or slightly asymmetric in cross-section, with a ventral groove from which two unequal flagella emerge. The plastid occupies a large portion of the cell and contains photosynthetic pigments including chlorophyll a, chlorophyll c, alpha-carotene, and phycobiliproteins, whose precise combination determines the cell's color. Cryptophytes including Chroomonas collegionis contribute to primary production in freshwater ecosystems and are grazed by heterotrophic flagellates and ciliates, linking microbial primary production to higher trophic levels. The species is part of the diverse microalgal flora of European freshwater bodies and has been documented in phycological surveys of the region. It has not been assessed under IUCN criteria.