A monograph on the Diphyllidea (Platyhelminthes: Cestoda)

Date of Completion

January 2001

Keywords

Biology, Molecular|Biology, Zoology

Degree

Ph.D.

Abstract

The main objective of this monograph was a synthesis of the available knowledge on the diversity, systematics, host associations and biogeography of the Diphyllidea. A thorough review of the literature resulted in the transfer of Diagonobothrium Shipley and Hornell, 1906 into Diphyllidea as a genus inquirendum. The genus Yogeshwaria Chincholikar and Shinde, 1976 was also transferred to Diphyllidea as a synonym of Echinobothrium. Its only species, E. nagabhushani n. comb. is considered a species inquirenda. New collections resulted in the description of a new species of Echinobothrium . Type and/or voucher specimens for 31 of 36 valid diphyllidean species (including the new species)were examined using light microscopy and scanning electron microscopy. All 31 species examined were redescribed and figured. This work resulted in the elucidation of 67 morphological characters which were employed in cladistic analyses involving 34 diphyllidean and seven outgroup species. Outgroups included species belonging to the orders Tetraphyllidea, Pseudophyllidea, and Trypanorhyncha. Several phylogenetic analyses were performed using various data partitions. A 20% exclusion rule was applied to both taxa and characters. All characters were treated as unweighted and unordered. Maximum parsimony was the optimality criterion used in all analyses. ^ The most parsimonious trees resulting from these analyses support Ditrachybothridiuln Rees, 1959 as a monophyletic taxon. All three species formerly assigned to Macrobothridium Khalil and Abdul-Salam, 1989 appeared among species of Echinobothrium. Thus, Echinobothrium is paraphyletic if Macrobothridium is excluded. As a consequence, Macrobothridium is synonymized with Echinobothrium, and its constituent species transferred into the latter genus. The trees obtained from these analyses failed to recover any of the topology of the only previously published phylogeny of the order. Constraining the tree resulting from this study into the topology of the previously published tree resulted in substantially longer tree length. ^ A comparison of the tree of the phylogenetic relationships among the diphyllideans with a composite tree of the relationships among batoid genera known to host Echinobothrium suggests that strict coevolution between the elasmobranchs and their diphyllidean tapeworms is unlikely to have occurred. However, because the sampling of potential elasmobranch hosts has not been comprehensive, this conclusion is considered preliminary. ^

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