nucleomorph

They are bound by four membranes and still possess a vestigial nucleus, called a nucleomorph.

Each is surrounded by four membranes, and there is a reduced cell nucleus called a nucleomorph between the middle two.

Cryptomonads and chlorarachniophytes retain the phagocytosed eukaryote's nucleus, an object called a nucleomorph, located between the second and third membranes of the chloroplast.

Because the nucleomorph lies between two sets of membranes, nucleomorphs support the endosymbiotic theory and are evidence that the plastids containing them are complex plastids.

The chloroplasts in euglenids and chlorarachniophytes were acquired from ingested green algae, and in the latter retain a vestigial nucleus (nucleomorph).

Whereas the nucleomorph in G. Theta supposedly came from a red algae, B. natans nucleomorph is likely the vestigal nucleus of a green algae.

These losses of function are hypothesized to have occurred at an early evolutionary stage in order to have allowed sufficient time for the complete degradation of acknowledged photosynthetic relicts and the disappearance of a nucleomorph.

They are surrounded by four membranes, the outermost of which is continuous with the endoplasmic reticulum, and contain a small nucleomorph between the middle two, which is a remnant of the alga's nucleus.

The endosymbiotic acquisition of a eukaryote cell is represented in the cryptophytes; where the remnant nucleus of the red algal symbiont (the nucleomorph) is present between the two inner and two outer plastid membranes.

Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus.

Some say that as long as there exists a gene in the nucleomorph that codes for proteins necessary for the plastid's functioning that are not produced by the host cell, the nucleomorph will persist.

The unique combination of host cell and complex plastid results in cells with four genomes: two prokaryotic genomes (mitochondrion and plastid of the red or green alga) and two eukaryotic genomes (nucleus of host cell and nucleomorph).

So far, only two groups of organisms are known to contain plastids with a vestigal nucleus or nucleomorph: the cryptomonads of the supergroup Chromista and the chlorarachniophytes of the supergroup Rhizaria, both of which have examples of sequenced nucleomorph genomes.

Studies of the genomic organization and of the molecular phylogeny have shown that the nucleomorph of the cryptomonads formerly was the nucleus of a red alga, whereas the nucleomorph of the chlorarchniophytes formerly was the nucleus of a green alga.