Relationships among nematodes based on the analysis of 18S rRNA gene sequences: molecular evidence for monophyly of chromadorian and secernentian nematodes

The relationships among nematodes were studied by 18S rRNA gene sequencing. On the basis of phylogenetic trees and cladistic analysis of the secondary structure of helix 49, some orders of traditional Adenophorea should be as cribed to the Secernentea. The Chromadorida and Desmodorida should be group ed with nematodes of a complex consisting of the Monhysterida, Plectida and Secernentea. This taxon may be named Chromadoria, as was proposed earlier (Drozdovsky, 1981), since chromadorids are most closely related to the comm on ancestor of these groups. Hence, the class Adenophorea in a traditional sense is paraphyletic and should be revised.