Selenastrum capricornutum

Raphidocelis subcapitata
Scientific classification
Domain:	Eukaryota
Kingdom:	Viridiplantae
Phylum:	Chlorophyta
Class:	Chlorophyceae
Order:	Sphaeropleales
Family:	Selenastraceae
Genus:	Raphidocelis
Species:	R. subcapitata
Binomial name
Raphidocelis subcapitata' (Korshikov) Nygaard, Komárek, J.Kristiansen & O.M.Skulberg

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.

...
Wikipedia