Unicelluar red algae with blue-greenish chloroplast. Most species inhabit in hot spring (high temperature, low pH). For Cyanidioschyzon merolae (NIES-1332), genome sequences of nucleus, chloroplast and mitochondrion have been reported.
Coccoid algae with cell wall possess single to many chloroplasts. Main photosynthetic pigment is C-phycocyanin. Golgi body is associated with ER. Asexual reproduction by binary fission or formation of endospores.