title: Molecular phylogeny, scale evolution and taxonomy of centrohelid heliozoa.
abstract: Heliozoa are ubiquitous, unicellular phagotrophs with slender radiating axopodia for trapping prey. We sequenced 18S rRNA genes from 35 cultured centrohelid heliozoa (18 studied by electron microscopy) and 28 environmental libraries (18 freshwater, 10 marine), yielding 97 new sequences, this exceeding described species. Phylogenetic analyses show two major groups and that ancestral centrohelids probably had inner plate-like tangential and distinct outer radial silica scales, the latter diverging early into contrasting scale types seen in extant Pterocystis/Choanocystis and Acanthocystis/Raphidiophryidae. Scales were lost at least thrice. Pterocystis is paraphyletic, as was the classical family Acanthocystidae; Heterophrys was polyphyletic. Using scale morphology and rRNA sequences, we establish new families Pterocystidae (Pterocystis, Raineriophrys, Chlamydaster), Marophryidae (type Marophrys (Heterophrys) marina gen. et comb. nov.) and Choanocystidae, new suborders Pterocystina (Pterocystidae, Choanocystidae, Heterophryidae) and Acanthocystina (Acanthocystidae, Raphidiophryidae, Marophryidae), and ten new Pterocystis, Acanthocystis and Choanocystis species. Most clades are exclusively freshwater or exclusively marine; evolutionary transitions between these habitats have been rare.
authors.affiliation: Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK. tom.cavalier-smith@zoo.ox.ac.uk
authors.forename: Thomas
authors.initials: T
authors.lastname: Cavalier-Smith
authors.forename: Sophie
authors.initials: S
authors.lastname: von der Heyden
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D016054:DNA, Protozoan / Q000235:genetics; D056890:Eukaryota / Q000145:classification* / Q000235:genetics* / Q000648:ultrastructure; D019143:Evolution, Molecular; D014644:Genetic Variation; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010802:Phylogeny; D016053:RNA, Protozoan / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics
chemical_list: D017931:DNA Primers; D016054:DNA, Protozoan; D016053:RNA, Protozoan; D012337:RNA, Ribosomal, 18S