Submitted to: Systematic Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 18, 1998
Publication Date: N/A
Interpretive Summary: A natural classification of the tapeworms, consistent with their phylogenetic history, provides the basis for an intimate understanding of host-parasite biology and distribution. Numerous lacunae in our knowledge of these parasites, however, continues to hinder advances in the development of modern classifications. Cladistic or phylogenetic analysis of the order Diphyllidea was conducted for the first time as a component of broader studies among the tapeworms. This analysis supported recognition of the order as a monophyletic group, and indicates that two rather than three genera are valid. Results are complementary to those for recent ordinal level phylogenetic studies of the tapeworms. The history of the diphyllideans has involved both cospeciation and colonization in elasmobranch (sharks and rays) fishes. The study serves as the basis for continued and more detailed analysis of the relationships of the tapeworms, and particularly those forms that are of potential importance in aquaculture and mariculture.
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 cladistics 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, Psuedophyllidea and Haplobothriidea. The phylogeny for the diphyllideans was found to be poorly resolved based on characters currently available for evaluation. Computer assisted cladistics analysis found 3 equally parsimonious trees with a consistency index of 0.54. The topology of these trees shows that Ditrachybothridium macrocephalus 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.