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

A phylogenetic analysis of tapeworms (Eucestoda) based on complete sequence s 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 p araphyletic) appeared as basal groups of the Eucestoda but their position w as not stable. The tetrafossate orders (Litobothriidea, Lecanicephalidea, T etraphyllidea, Proteocephalidea, Nippotaeniidea, Tetrabothriidea and Cyclop hyllidea) were well separated from the remaining groups. Results supported polyphyly of the Pseudophyllidea formed by two distinct clades: one with di phyllobothriids (Diphyllobothrium, Schistocephalus, Spirometra and Duthiers ia) and another including Abothrium, Probothriocephalus, Eubothrium and Bot hriocephalus. The former pseudophyllidean clade formed a separate branch wi th the Caryophyllidea (Khawia and Hunterella) and Haplobothriidea (Haplobot hrium), the latter taxon being closely related to either caryophyllideans o r diphyllobothriids in different analyses. Proteocephalideans formed a mono phyletic group in all analyses and constituted a clade within the Tetraphyl lidea thus rendered paraphyletic. Within the Proteocephalidea, the Acanthot aeniinae (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 specie s, Monticellia sp., in a clade within the former family. The genus Proteoce phalus appeared as an artificial assemblage of unrelated taxa which is cong ruent with previous molecular analyses. (C) 2000 Australian Society for Par asitology Inc. Published by Elsevier Science Ltd. All rights reserved.