Inference of phylogeny and taxonomy within the Didymozoidae (Digenea) fromthe second internal transcribed spacer (ITS2) of ribosomal DNA

DNA sequences of the second internal transcribed spacer (ITS2) of ribosomal DNA (rDNA) were determined for 11 species from four genera of Didymozoinae (Indodidymozoon, Helicodidymozoon, Rhopalotrema and Neometadidymozoon) and a species of the Lecithasteridae, Lecithaster stellatus. Sequences were us ed to test the validity of species recognised on morphological criteria and to infer phylogenetic relationships. Sequences of the 11 didymozoids diffe red by 0.5% to 19%. Our phylogenetic analyses: (i) indicate that species in the genera Helicodidymozoon and Rhopalotrema are a monophyletic group; (ii ) support separation of the genus Helicodidymozoon from the genera Indodidy mozoon and Neometadidymozoon; and (iii) support recognition of Rhopalotrema as a genus distinct from Neometadidymozoon. We found the gonochoristic spe cies, I. pearsoni and I. suttiei, to be genetically similar to the hermaphr oditic species in the genus Indodidymozoon and found no evidence to indicat e that they belong in a separate genus.