Cryptomonads

Cryptomonads are aquatic unicellular eukaryotes that live in both marine and freshwater environments, and most are photosynthetic, in which case they are called cryptophytes. Their plastids vary widely in pigmentation. Cryptophytes acquired photosynthesis through secondary endosymbiosis, engulfing and assimilating a red algal endosymbiont, so each cell has a four-membrane-bound plastid and four DNA-containing compartments: the plastid, the mitochondrion, the host nucleus and the endosymbiont nucleus, called the nucleomorph. The nucleomorph genome is highly reduced and is studied to understand how secondary endosymbiosis works.