The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally they have the form of small amoebae, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net. These extensions are dependent on the presence of light and polymerization of the actin cytoskeleton. They may also form flagellate zoospores, which characteristically have a single subapical flagellum that spirals backwards around the cell body, and walled coccoid cells. The chloroplasts were presumably acquired by ingesting some green alga. 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. This contains a small amount of DNA and divides without forming a mitotic spindle. The origin of the chloroplasts from green algae is supported by their pigmentation, which includes chlorophylls a and b, and by genetic similarities. The only other groups of algae that contain nucleomorphs are a few species of dinoflagellates, which also have plastids originating from green algae, and the cryptomonads, which acquired their chloroplasts from a red alga. The chlorarachniophytes only include five genera, which show some variation in their life-cycles and may lack one or two of the stages described above. Genetic studies place them among the Cercozoa, a diverse group of amoeboid and amoeboid-like protozoa. The chlorarachniophytes were placed before in the order Rhizochloridales, class Xanthophyceae (e.g., Smith, 1938), as algae, or in order Rhizochloridea, class Xanthomonadina (e.g., Deflandre, 1956), as protozoa. So far sexual reproduction has only been reported in two species; Chlorarachnion reptans and Cryptochlora perforans.

Morphology

[[File:2023 Chlorarachniophyte.svg|center|thumb|upright=2|Representation of a Chlorarachniophyte1. Filopodium 2. Extrusomes 3. Mitochondrion, creates ATP (energy) for the cell (flat cristae) 4. Capping vesicle 5. Golgi apparatus, modifies proteins and sends them out of the cell 6. Nucleomorph 7. Plastid membranes (4, secondary green) 8. Stacked thylakoid, site of the light-dependent reactions of photosynthesis 9. Pyrenoid, center of carbon fixation 10. Globules 11. Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell 12. Nucleolus 13. Nucleus 14. Prey in phagosome 15. Digestive vacuole]]

Phylogeny

Based on Shiratori et al. 2024.

Taxonomy