Morphological and genetic analysis of a rediscovered Clinostomum sp. parasitising Titanolebias monstrosus and Trigonectes aplocheiloides (Cyprinodontiformes: Rivulidae)

Abstract

Clinostomids are a group of digeneans in which substantial diversity has been recently discovered,with some metacercariae specific to their fish hosts. Genetic analysis has been instrumental inelucidating species diversity within this genus. Recently, seven COI lineages were reported inArgentina, along with three metacercarial morphotypes lacking molecular data. Two of thesewere found parasitising Rivulidae fishes. The discovery of Clinostomum metacercariae in Trigo-nectes aplocheiloides and Titanolebias monstrosus from temporary ponds in the western Chacoanregion allowed us to redescribe the metacercariae previously identified by other authors andprovide the first sequences of this lineage. The morphology of the metacercariae in both hostsmatched previously reported descriptions. Genetic analysis clustered the new lineage withClinostomum detruncatum, Clinostomum sp. 7, Clinostomum L1, and Clinostomum CRA. Thisdiscovery leaves only two morphological records of metacercariae to be characterised using DNAsequencing: one in another Rivulidae (Neofundulus paraguayensis) and one in a Loricaridae(Hypostomus sp.). The present results represent the eighth clinostomid lineage sequenced fromArgentina, highlighting the extensive diversity in South America and the many lineages yet to bedescribed or identified, considering that only one of these lineages is formally described based onadult specimens found in the heron Ardea cocoi.