Raphidocelis subcapitata, formerly known as Selenastrum capricornutum and Pseudokirchneriella subcapitata is a microalga. This microalga presents a curved and twisted appearance like a sickle. The cells are normally presented in a solitary form. It has a length between 8 and 14 µm, and a width between 2 and 3 µm. It is commonly used as a bioindicator species to assess the levels of nutrients or toxic substances in freshwater environments. This species is quite sensitive to the presence of toxic substances including metals and has a ubiquitous distribution, so is broadly used in ecotoxicology.