Systematics of Onchocleidus Mueller, 1936 (Monogenea: Ancyrocephalidae): phylogenetic relationships, evolution, and host associations

Abstract

The phylogeny of Onchocleidus Mueller, 1936 (sensu Wheeler and Beverley-Burton 1989) is analysed cladistically. The putative monophyly of the genus is supported by three synapomorphies: dextral vaginal opening, spiral filament encircling the penis, and dorsal hamuli with reduced deep roots. Haplocleidus Mueller, 1937 and Pterocleidus Mueller, 1937 are considered synonyms of Onchocleidus. The spiral filament, previously considered synapomorphic for the group comprising Onchocleidus and Aethycteron Suriano and Beverley-Burton, 1982, is reinterpreted as independently derived in both genera. An alternative hypothesis is presented for the relationship between Onchocleidus and Aethycteron, with the spiral filament and accessory piece of Aethycteron arising through transformation of an accessory piece similar to that found in Urocleidus Mueller, 1934. This implies a sister-group relationship between Aethycteron and Urocleidus, not between Aethycteron and Onchocleidus. The host associations of Onchocleidus, Aethycteron, and Urocleidus are discussed in light of this hypothesis. Onchocleidus is assumed to have originated and (or) radiated on centrarchids; species of Onchocleidus parasitizing Percichthyidae are not monophyletic and probably spread to percichthyids via ecological association. Rather than assume that Aethycteron spread to percids by ecological association with centrarchids, it appears that percids were host to a common ancestor of Aethycteron and Urocleidus, which later radiated, giving rise to the two genera. The occurrence of Urocleidus on centrarchids is attributed to ecological association with percids.