Re-evaluation of the taxonomic status of taxa recognized within the expanded concept of Sphincteristomum Oshmarin, Mamaev & Parukhin, 1961 and the related Lobatotrema Manter, 1963 (Digenea: Megaperidae).

The taxonomic status of Sphincteristomum Oshmarin, Mamaev & Parukhin, 1961 (sensu lato) and Lobatotrema Manter, 1963 is controversial due to overlap/confusion in distinctive diagnostic characteristics for each genus and morphological/allometric ambiguity among some of their representatives and/or within records of the same species. To address these in-depth, morphological descriptions, molecular characterizations, and species delimitation analyses were conducted using a combination of comparative morphology, molecular phylogeny, multivariate analyses, and host-parasite data. Following a comprehensive review, a refined restricted concept of Sphincteristomum and Lobatotrema is proposed. Representatives of Lobatotrema comprise Lobatotrema aniferum Manter, 1963 (sensu lato) and the morphologically/phylogenetically distinct Lobatotrema dronenin. sp. Representatives of Sphincteristomum (sensu stricto) include Sphincteristomum acollum Oshmarin, Mamaev & Parukhin, 1961, and Sphincteristomum nikolaevi Parukhin, 1970. The taxonomic status of Sphincteristomum mediterraneae Abid-Kachour, Mouffok & Boutiba, 2013 is problematic based on its intermediate taxonomic position between the Megaperinae Manter, 1934 and the Schistorchiinae Yamaguti, 1942. Molecular datasets are employed in an attempt to delineate and interpret more phylogenetic relationships among schistorchiines in light of differences in oral sucker nature, oral sucker shape, and oral sphincter shape. Distributions of schistorchiines in the Indo-West Pacific are discussed. Testes arrangement as a characteristic in this group and glandular components within a muscular oral sucker are presented. We comment on the close phylogenetic relationship between members of the Schistorchiinae and the Megaperinae.