Inferring a classification of the Adenophorea (Nematoda) from nucleotide sequences of the D3 expansion segment (26/28S rDNA)

Nucleotide sequences of the D3 expansion segment of the 28S rDNA gene were used to reconstruct evolutionary relationships within the Adenophorea. Neighbor-joining and parsimony analyses of representatives of most major taxa revealed a paraphyletic Adenophorea (p = 0.0005). Within Adenophorea, the Enoplia, Enoplida, and Enoplina were paraphyletic (p = 0.0024, 0.0014, and 0.0120, respectively). A major division was evident within the Enoplida, with one lineage consisting of a basal Thoracostomopsidae and Enoplidae, and a second lineage consisting of Oncholaimidae and Encheliididae. Tripyloidina clustered close to the basal enoplid branch and formed a monophyletic taxon. Although appearing as paraphyletic in the maximum-parsimony and neighbor-joining trees, constraining Chromadoria and Chromadorida into monophyletic groups did not result in a longer tree. Within the Chromadoria, the order Desmodorida sensu Malakhov (1994) was paraphyletic. However, Desmodorida sensu Lorenzen (1994), which does not include Ceramonematidae, was monophyletic. Monhysterida formed a monophyletic order within Chromadoria, equivalent to Chromadorida and Desmodorida. The position of the Comesomatidae was tentatively identified among the Chromadorida, however, the possibility of their placement among the Monhysterida cannot be excluded completely.