On the phylogenetic relationships among tetraphyllidean, lecanicephalideanand diphyllidean tapeworm genera

This study had two main objectives: (1) to construct an extensive, explicit list of characters and character states that might serve as a starting poi nt, and perhaps even a model, for the compilation of a more complete list o f characters for all cestode taxa; and (2) to use this character list to ge nerate a hypothesis of the phylogenetic relationships among species represe nting most of the tetraphyllidean, lecanicephalidean and diphyllidean gener a. Specimens of one species in each of 48 genera of tetraphyllideans, eight genera of lecanicephalideans, the three genera of diphyllideans, two gener a of proteocephalideans and two genera of trypanorhynchs, were examined as whole-mounts and sections, with light and scanning electron microscopy. A l ist of 120 morphological characters was compiled. Four phylogenetic analyse s were conducted using PAUP* and/or NONA. The first was a comprehensive ana lysis with the 56 tetraphyllidean and lecanicephalidean species as ingroups and the remaining seven species as outgroups. The second was an analysis o f the three diphyllidean species as ingroups and the two proteocephalidean and the two trypanorhynch species as outgroups. The third was an analysis o f the eight lecanicephalidean species and the "tetraphyllideans" Echeneibot hrium sp. and Pseudanthobothrium n. sp. as ingroups and an outgroup consist ing of the seven species used as outgroups in the first analysis. In the fo urth analysis, the ingroup consisted of the 14 hooked tetraphyllideans (onc hobothriids), and the outgroup consisted of the seven species used as outgr oups in the first analysis. The results of these analyses support the follo wing phylogenetic hypotheses: The diphyllideans are monophyletic and Echino bothrium n. sp, and Macrobothridium sp. are more closely related to one ano ther than either is to Ditrachybothridium macrocephalum. The tetraphyllidea ns, lecanicephalideans and proteocephalideans are more closely related to e ach other than they are to the diphyllideans or the trypanorhynchs. The ord inal status of the lecanicephalideans is dubious. The lecanicephalidean spe cies are more closely related to some of the tetraphyllidean taxa than thes e tetraphyllidean taxa are to the remainder of the tetraphyllidean tare. Th e proteocephalideans appear to belong within the tetraphyllidean clade. The "tetraphyllidean" species Echeneibothrium sp. and Pseudanthobothrium n. sp . are members of the lecanicephalidean clade. The position of "Discobothriu m" n. sp. within the lecanicephalideans is dubious. Within the tetraphyllid eans, the non-acetabulate species Litobothrium daileyi, Disculiceps galapag oensis and Cathetocephalus sp. are the most basal members of the group. The family Onchobothriidae is monophyletic, as it is currently defined. Within the onchobothriids, the uniloculate species are basal to the multiloculate species; the species with unipronged hooks are basal to the species with m ultipronged hooks. Although relationships among the phyllobothriids. as the y are currently defined, remain poorly resolved, the family Phyllobothriida e is not monophyletic, These results suggest that some aspects of the class ification of the lecanicephalidean and tetraphyllidean taxa require revisio n. However, such revision should be based on further analyses including a b roader representation of the genera and species in these groups.