Molecular phylogeny, scale evolution and taxonomy of centrohelid heliozoa
- 作者：Thomas Cavalier-Smith ; Sophie von der Heyden
- 关键词：18S rRNA ; Acanthocystina ; Centrohelid heliozoa ; Freshwater/marine divergence ; Pterocystina ; Silica scales
- 刊名：Molecular Phylogenetics and Evolution
- 出版年：2007
- 期刊代码：176_10557903
- 类别：bio
- 出版时间：September 2007
- 卷：44
- 期：3
- 页码：1186-1203
- 文件大小：1707 K
摘要
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.