Relationships within the Acanthocolpidae Luhe, 1906 and their place among the Digenea

The phylogeny of the Acanthocolpidae, a family of marinejlsh parasites, was assessed using SSU and LSU rDNA and combined sequences of thirteen putative species. Cableia púdica is found to be a basal monorchiid, not an acanthocolpid. The remaining species form a monophylum only if the marine mammal parasite, the brachycladiid Zalophotrema hepaticum is included. The Acanthocolpidae comprises two clades (Zalophotrema (Pleorchis, Tormopsolus)) and (Stephanostomum). Some morphological similarities were detected between Zalophotrema and Pleorchis, but Tormopsolus is morphologically more similar to Stephanostomum. Nine species of the large genus Stephanostomum were studied, including two species from two host species each, and the relationships inferred from the analysis of sequences were poorly reflected in morphological or biological characteristics. Evidence from sister taxa indicates that the parasites of piscivorous marine mammals, the Brachycladiidae, are derived from piscivorous marine fish parasites.