Chlorarachniophytes

Abstract

The chlorarachniophytes are a group of single-celled phototrophic, mixotrophic eukaryotes in marine environments. They are most common in tropical and temperate seas. The group is primarily studied due to their evolutionary history. Chlorarachniophytes acquired photosynthesis by secondary endosymbiosis, where an amoeboflagellate host took up a green algal symbiont and retained it. The symbiont is distinguished by having retained a relict nucleus, or nucleomorph, which has been intensively studied to help elucidate the process of organelle origins by endosymbiosis. Historically, work on the nucleomorph was an important clue suggesting that secondary endosymbiosis played a role in the distribution of photosynthesis and plastids in eukaryotes. More recently, a number of genomic and cell biological studies, in particular focusing on gene flow within the cell and protein targeting, have further contributed to our under- standing of organelle integration during endosymbiosis. The host component is now known to be a member of the Cercozoa and can include amoeboid, flagellate, and cyst stages, various species having any combination of one or more stages in the life cycle.