nucleomorph

Nucleomorphs are small, reduced eukaryotic nuclei found in certain plastids. So far, only two groups of organisms are known to contain a nucleomorph: the cryptomonads of the supergroup Chromista and the chlorarachniophytes of the supergroup Rhizaria, both of which have examples of sequenced nucleomorph genomes.

The nucleomorphs support the endosymbiotic theory, and are an evidence that the plastids of these organisms are so-called complex plastids.