The taxonomy of the family Xyalidae Chitwood, 1951 (Monhysterida: Nematoda): A cladistic analysis

A cladistic analysis of the family Xyalidae has been carried out, with selected Monhysteridae and Sphaerolaimidae as presumptive outgroups. Forty nine characters, taken from published descriptions, were scored for 91 species from 33 genera. The way in which the characters were coded is illustrated by drawings and graphs. Phylogenetic analyses were conducted with the programs PAUP*4.0d65 and PAUP*4.0b2. Neighbour-joining and parsimony trees were constructed and the preferred consensus parsimony tree is presented. The tree has been divided into 15 groups for purposes of discussion. All eight species of Monhysteridae form a separate clade consistent with outgroup status, but the four species of Sphaerolaimidae are not separated from Xyalidae. Several of the Daptonema species, Pseudosteineria plus Steineria, and Rhynchonematinae form three well supported clades. Other groupings are much less well supported and are presumed to be paraphyletic. Many published descriptions do not include sufficient detail to allow relationships to be determined and suggestions are made as to data which should be included in future taxonomic descriptions of Xyalidae.