chlorarachniophytes

Chlorarachniophytes are a group of unicellular, photosynthetic protists in the Rhizaria lineage, commonly placed in the class Chlorarachniophyceae. They are mainly marine, with some species occurring in freshwater, and are notable for combining photosynthesis with phagotrophy in a single organism. Their cells are typically amoeboid in morphology and display reticulopodial pseudopods that form an interconnected network used for movement and prey capture.

A defining feature of chlorarachniophytes is their plastid, which arose through secondary endosymbiosis of a green alga. The plastid is surrounded by four membranes and contains a nucleomorph, a remnant nucleus of the engulfed green alga housed in the periplastidial space. This nucleomorph is a key piece of evidence for the history of secondary endosymbiosis. The plastids of chlorarachniophytes contain chlorophylls a and b and enable photosynthesis, while the organisms can also acquire nutrients by ingesting prey.

In addition to their distinctive plastids, chlorarachniophytes are studied for their cellular organization and evolutionary history. The model species Bigelowiella natans has been used to investigate plastid evolution, nucleomorph genomes, and endosymbiotic gene transfer. Ecology-wise, chlorarachniophytes are distributed worldwide in coastal and open-ocean waters and can contribute to microbial food webs as mixotrophs, balancing photosynthesis with heterotrophic feeding depending on environmental conditions.

Taxonomically, they are a part of Rhizaria and include genera such as Chlorarachnion and Bigelowiella. Their unique plastid-nucleomorph system makes them important for studies of plastid evolution and secondary endosymbiosis.