On the phylogenetic positions of the Caryophyllidea, Pseudophyllidea and Proteocephalidea (Eucestoda) inferred from 18S rRNA.

A phylogenetic analysis of tapeworms (Eucestoda) based on complete sequences of the 18S rRNA genes of 43 taxa (including new sequences of 12 species) was carried out, with the emphasis on the groups parasitising teleost fish and reptiles. Spathebothriidea and Trypanorhyncha (the latter group being paraphyletic) appeared as basal groups of the Eucestoda but their position was not stable. The tetrafossate orders (Litobothriidea, Lecanicephalidea, Tetraphyllidea, Proteocephalidea, Nippotaeniidea, Tetrabothriidea and Cyclophyllidea) were well separated from the remaining groups. Results supported polyphyly of the Pseudophyllidea formed by two distinct clades: one with diphyllobothriids (Diphyllobothrium, Schistocephalus, Spirometra and Duthiersia) and another including Abothrium, Probothriocephalus, Eubothrium and Bothriocephalus. The former pseudophyllidean clade formed a separate branch with the Caryophyllidea (Khawia and Hunterella) and Haplobothriidea (Haplobothrium), the latter taxon being closely related to either caryophyllideans or diphyllobothriids in different analyses. Proteocephalideans formed a monophyletic group in all analyses and constituted a clade within the Tetraphyllidea thus rendered paraphyletic. Within the Proteocephalidea, the Acanthotaeniinae (Acanthotaenia from reptiles in Africa) and Gangesiinae (Gangesia and Silurotaenia from silurid fish in the Palearctic Region) were separated from parasites of freshwater fish and mammals. The family Proteocephalidae was found to be paraphyletic due to the placement of a monticelliid species, Monticellia sp., in a clade within the former family. The genus Proteocephalus appeared as an artificial assemblage of unrelated taxa which is congruent with previous molecular analyses.