Phylogenetic relationships of the monozoic tapeworms (Eucestoda: Caryophyllidea) inferred from morphological characters.

Phylogenetic relationships of all genera of the order Caryophyllidea, possibly the earliest branching group of true tapeworms (Platyhelminthes: Eucestoda) and the only one that is monozoic, have been assessed for the first time. Results of this cladistic analysis, inferred from 30 unweighted morphological characters, are only partly congruent with the existing classification, which consists of four families based on the position of the inner longitudinal muscles in relation to the internal genital organs. Whereas all but five genera of the Caryophyllaeidae form a monophyletic clade, members of the Capingentidae are split, occurring within six unrelated groups. The Lytocestidae is also paraphyletic, as some genera appear in four unrelated clades. Archigetes appears in a derived clade, indicating that its direct (monoxenous) life-cycle involving only tubificid oligochaetes is secondarily derived and not plesiomorphic among the Eucestoda, as postulated by some authors.