A new species of Auriculostoma (Digenea:Allocreadiidae) in South America: life cycle and phylogenetic relationships

Abstract

Auriculostoma is a Neotropical distributed genus of flatwormsflatworm's digeneans whose adults are parasites of freshwater fishes. We describe the new species Auriculostoma ocloya using morphological and molecular tools, and elucidate its life cycle, the first known of a species of this genus. The first intermediate host is the bivalve Pisidium ocloya, the second intermediate host is the amphipod Hyalella sp., and the definite hosts are siluriform fishes. The adult presents a single pair of muscular lobes on either side of the oral sucker with a broad base, stretching from ventrolateral to dorsolateral, structure also present in the rest of species of the genus. Nevertheless, the new species is set apart from all congeners because the posterior ?free? ends of the lobes are not present in our specimens. This is the first study to provide sequence data from larval and adult stages of Auriculostoma species in South America. Our analyses demonstrated the basal position and strong separation of the new specie from other members of the genus likely reflects the ancient nature of their host association. Our study even with limited data allowed us to reveal important trends in the evolution of their morphological traits, host associations and geographic distribution.