title: Monophyly of the family Desmoscolecidae (Nematoda, Demoscolecida) and its phylogenetic position inferred from 18S rDNA sequences.
abstract: To infer the monophyletic origin and phylogenetic relationships of the order Desmoscolecida, a unique and puzzling group of mainly free-living marine nematodes, we newly determined nearly complete 18S rDNA sequences for six marine desmoscolecid nematodes belonging to four genera (Desmoscolex, Greeffiella, Tricoma and Paratricoma). Based on the present data and those of 72 nematode species previously reported, the first molecular phylogenetic analysis focusing on Desmoscolecida was done by using neighbor joining (NJ), maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods. All four resultant trees consistently and strongly supported that the family Desmoscolecidae forms a monophyletic group with very high node confidence values. The monophyletic clade of desmocolecid nematodes was placed as a sister group of the clade including some members of Monhysterida and Araeolaimida, Cyartonema elegans (Cyartonematidae) and Terschellingia longicaudata (Linhomoeidae) in all the analyses. However, the present phylogenetic trees do not show any direct attraction between the families Desmoscolecidae and Cyartonematidae. Within the monophyletic clade of the family Desmoscolecidae in all of the present phylogenetic trees, there were consistently observed two distinct sub-groups which correspond to the subfamilies Desmoscolecinae [Greeffiella sp. + Desmoscolex sp.] and Tricominae [Paratricoma sp. + Tricoma sp].
authors.affiliation: Department of Biology, Teachers College and Department of Biology, Graduate School, Kyungpook National University, Daegu 702-701, Korea.
authors.forename: Ui Wook
authors.initials: UW
authors.lastname: Hwang
authors.forename: Eun Hwa
authors.initials: EH
authors.lastname: Choi
authors.forename: Dong Sung
authors.initials: DS
authors.lastname: Kim
authors.forename: Wilfrida
authors.initials: W
authors.lastname: Decraemer
authors.forename: Cheon Young
authors.initials: CY
authors.lastname: Chang
mesh_terms: D000818:Animals; D001483:Base Sequence; D001499:Bayes Theorem; D003198:Computer Simulation; D004275:DNA, Ribosomal / Q000032:analysis*; D019143:Evolution, Molecular; D049810:Genetic Speciation; D008969:Molecular Sequence Data; D009348:Nematoda / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D054682:Ribosome Subunits, Small, Eukaryotic / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D004275:DNA, Ribosomal