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. Neig hbor-joining and parsimony analyses of representatives of most major taxa r evealed a paraphyletic Adenophorea (p = 0.0005). Within Adenophorea, the En oplia, 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 D esmodorida sensu Malakhov (1994) was paraphyletic. However, Desmodorida sen su Lorenzen (1994), which does not include Ceramonematidae, was monophyleti c. Monhysterida formed a monophyletic order within Chromadoria, equivalent to Chromadorida and Desmodorida. The position of the Comesomatidae was tent atively identified among the Chromadorida, however, the possibility of thei r placement among the Monhysterida cannot be excluded completely.