Phylogenetic analysis of rDNA sequences from adenophorean nematodes and implications for the Adenophorea-Secernentea controversy

Phylogenetic relationships of 13 adenophorean and 15 secernentean nematodes were analyzed using morphological data and 18S rDNA sequences in parallel. Both data sets strongly supported monophyly of Adenophorea and Secernentea. Monophyly of the subfamily Stilbonematinae-which is remarkable for symbiosis with bacteria-was also confirmed. Three taxa without symbionts (Desmodora, Xyzzors, and Acanthopharynx) branched at the base of the adenophoreans. Enoplus meridionalis, representing the Enoplida, was distantly related to the remaining adenophoreans and formed their most basal branch. All analyses also supported monophyly of the genera Embostrichus, Laxus, Haemonchus, and Caenorhabditis. Within the secernenteans, the genus Rhabditis, however, appeared to be paraphyletic with respect to the genus Rhabditella.