Monophyly of the family Desmoscolecidae (Nematoda, Demoscolecida) and its phylogenetic position inferred from 18S rDNA sequences

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].

A New Marine Nematode Species of the Genus Dinetia (Nematoda: Draconematidae) from South Korea

A new draconematid nematode species of the genus Dinetia Decraemer and Gourbault, 1997 is described from the subtidal sediments and small logs from the eastern coast of South Korea. Dinetia orientalis n. sp. mainly differs from D. nycterobia Decraemer and Gourbault, 1997 by the following characters: large number of cephalic adhesion tubes (38-42 in male and 37-40 in female), number of posterior sublateral adhesion tubes (9-11 in male and 13-14 in female) and posterior subventral adhesion tubes (17-22 in male and 19-24 in female), the buccal cavity (narrow and armed with a dorsal and two weak ventrosublateral teeth), spicules (strongly arcuated and with a pair of strongly dilated gubernaculums around distal part of spicules), and higher "c" value (8.3-10.4 in male and 8.5-10.7 in female). This is the first report on free-living marine nematodes from South Korea, and the first record of the genus Dinetia in the Northwest Pacific.