ABSTRACT
Advances in our understanding of genealogy among the orders of the Eucestoda have been based on independent approaches linked to comparative morphology and analysis of molecular sequence data, particularly from 18S rDNA. Parsimony analyses of molecular or morphological databases have yielded largely concordant trees supporting monophyly for the Eucestoda: 1) monozoic Caryophyllidea are basal; 2) difossate and segmented forms such as Pseudophyllidea are the sister for the remaining orders; and 3) tetrafossates including the para-phyletic Tetraphyllidea, Proteocephalidea, Nippotaeniidea, Tetrabothriidea, Mesocestoidata, and Cyclophyllidea are highly derived. Hypotheses by Hoberg et al. (1997c) and Mariaux (1998) differed in placement of the Diphyllidea and the Trypanorhyncha. A 'total evidence' approach now combines substantial components of currently available morpho- logical and molecular data and additional taxa to further examine the putative relationships among the Eucestoda using two complementary strategies: 1) a top-down analysis employing a 'consensus' or reduced matrix for molecular and morphological data for the ingroup across 11 ordinal-level taxa, three families of Tetraphyllidea and two families of Pseudophyllidea; and 2) a bottom-up analysis employing character data for individual, representative genera and species including 48 ingroup taxa across 16 ordinal and family-level taxa in a 'comprehensive' matrix. Parsimony analysis of the consensus matrix resulted in two most-parsimonious trees (MPTs) (CI = 0.671, RC = 0.378) largely similar to general structure outlined by Hoberg et al. (1997c) and Mariaux (1998). Analysis of the comprehensive matrix resulted in 48 equal-length trees (CI = 0.484, RC = 0.378) congruent to the MPTs derived from analysis of the consensus matrix in diagnosing the orders and putative relationships of the eucestodes. Results overall contrasted minimally with Hoberg et al. (1997c) or Mariaux (1998). Comparative data from morphology, ontogeny and ultrastructure are validated; a complementary nature is emphasized for: 1) morphological and molecular characters; and 2) top-down versus bottom-up approaches. Phylogenetic resolution among the Eucestoda will lead to development of model systems for evolutionary biology, cospeciation analysis and historical biogeography.
