Proterometra epholkos sp. n. (Digenea: Azygiidae) from Terrapin Creek, Alabama, USA: Molecular characterization of life cycle, redescription of Proterometra albacauda, and updated lists of host and geographic locality records for Proterometra spp. in North America

Abstract

Proterometra epholkos sp. n. asexually reproduces in the stream dwelling prosobranch, Elimia cf. modesta (Cerithioidea: Pleuroceridae) and infects the buccal cavity epithelium of spotted bass, Micropterus punctulatus (Perciformes: Centrarchidae) in the Coosa River (Terrapin Creek; N33°51′36.56″, W85°31′28.15″; Cleburne County, Alabama, USA). We characterize cercariae and adults of the new species using morphology and molecular sequence data and redescribe its morphologically similar congener Proterometra albacauda based on the holotype and paratype (USNPC Nos. 61229-30). The new species can be distinguished most easily from P. albacauda by the combination of having cercariae with long mamillae (>100μm) that encircle the tail stem anteriorly, that are restricted to 1 lateral column per body margin at midbody, and that are absent from the medial surface of the tail stem as well as by having adults with a partly extracecal uterus, a transverse metraterm occupying the space between the oral sucker and prostatic sac, and a vitellarium that is longer than the ceca and extends anteriad to the level of or beyond the posterior margin of the oral sucker. Sequence data from the ribosomal internal transcribed spacer 2 (ITS2; 251bp) did not reject the notion that the cercariae and adults we collected simultaneously from those infected, sympatric, individual snails and fish in Terrapin Creek were conspecific. Also provided herein for species of Proterometra are (i) taxonomic keys for cercariae and adults based on morphological and behavioral characteristics sourced from the published literature, (ii) updated lists of host records (prosobranchs and fishes) and geographic locality records for Proterometra spp., and (iii) synopses and assessments of the morphological features previously used to differentiate them. Proterometra macrostoma (type species), Proterometra melanophora, and Proterometra hodgesiana are species inquirendae; requiring new collections from type localities and hosts concomitant with neotype designations. P. macrostoma seems a repository for conspicuous, furcocystocercous cercariae shed from freshwater prosobranchs in eastern North American rivers and streams. The specific epithet “pinguis” associated with specimens purportedly infecting Esox lucius and deposited by JF Mueller is a nomen nudum. Proterometra guangzhouensis, Proterometra sillagae, Proterometra brachyuran, and Proterometra lamellorchis are incertae sedis. Significant barriers to characterizing biodiversity and distributions (host range and geographic distribution) of Proterometra spp. comprise a paucity of data on adult morphology, dubious species-level identification or a lack of information regarding prosobranch hosts, lack of molecular data for putative comparisons among fluke ‘strains’ and species as well as between cercariae and adults, lack of consistency in terminology, and indeterminate homology for key morphological features. Uncertainty about the providence and identity of, or absence of, accessioned museum materials of P. macrostoma, Proterometra catenaria, and P. hodgesiana together represent another fundamental problem. The present study comprises the first description of a new species of Proterometra in nearly 20years, first report of a species of the genus from the Coosa River (Mobile–Tensaw River Basin) and from these host species, and first use of molecular sequence data to elucidate a life cycle for a species of Proterometra.