Contain chlorophyll a , carotenoids, phycobilins, and chlorophyll d in some. Red color of plastids due to the accessory pigment, phycoerythrin. Phycoerythrin is a phycobilin, a pigment found only in red algae and cyanobacteria. Deep water forms are almost black, moderate depth forms are red, and shallow water forms are green. One species has been discovered near the Bahams at a depth of 260 meters.
Some tropical species lack pigmentation and survive as parasites on other red algae.