Preliminary comments on a phylogenetic study of the order Diphyllidea van Beneden in Carus, 1863.

The basis for a preliminary analysis of the relationships within the monophyletic Diphyllidea is outlined. Information on morphological characters and their interpretation within a phylogenetic context are presented. A cladistic analysis at the species level was conducted based on a matrix of 21 morphological characters. Character polarity was determined by taxonomic outgroup analysis relative to the basal orders, Pseudophyllidea and Haplobothriidea. The phylogeny for the diphyllideans was found to be poorly resolved based on characters currently available for evaluation. Computer assisted cladistic analysis found three equally parsimonious trees with a consistency index of 0.54. The topology of these trees shows that Ditrachybothridium macrocephalum is the basal taxon and the putative sister group for species of Echinobothrium; Macrobothridium rhynchobati is grouped among species of Echinobothrium. If the classification is to be consistent with this tree, M. rhynchobati should be included in the genus Echinobothrium. This observation should be carefully examined, considering the relative paucity of useful morphological characters currently available for this group.