Corallochytrium, an enigmatic non-flagellate protozoan related to choanoflagellates

Corallochytrium limacisporum is an unusual non-flagellate, saprotrophic marine protist of no known affinities. Though originally described as a thraustochytrid, it has no morphological characters that specifically link it to thraustochytrids, or to fungi, or to any well-established protist group. We have cloned and sequenced its 18s rRNA gene, and carried out a phylogenetic analysis by four different methods. These unequivocally show that Corallochytrium is not a thraustochytrid, but is instead specifically related to choanoflagellate protozoa and to the enigmatic rosette agent of salmon. A new family, Corallochytriidae, is established to accommodate it. Corallochytrids clearly belong within the protozoan phylum Choanozoa but in a distinct order, Corallochytrida Cavalier-Smith 1995, and class, Corallochytrea Cavalier-Smith 1995.