A group of single-celled algae characterized by a “nucleomorph,” sandwiched between the membranes that surround the chloroplast. Cryptomonads are thought to have arisen hundreds of millions of years ago by the fusion of a red algal symbiont and a biflagellated protozoan. The protozoan was the source of the conventional nucleus, whereas the nucleomorph is all that remains of the symbiont's nucleus. It contains three minute linear chromosomes with telomeres and densely packed genes and is surrounded by a double envelope with characteristic pores. Nucleomorphs represent nuclei that have undergone the greatest genomic reduction in the history of eukaryotes, See Classification, Protoctista, Cryptomonada; Chronology, 1999, Beaton and Cavalier-Smith; C value paradox, serial symbiosis theory, skeletal DNA hypothesis.
Subjects: Genetics and Genomics.