A revision of the poorly known Pontocaspian gastropod genus Abeskunus, and its Central Paratethyan origin

Abstract

ABSTRACT Biodiversity and conservation assessments rise and fall with taxonomic accuracy. An example of a still largely unresolved taxonomy is found in the Gastropoda of the Caspian Sea. The present paper clarifies the taxonomy of the genus Abeskunus and its three species of anomalohaline gastropods endemic to the Caspian Sea. Based on material from Pleistocene, Holocene, and (sub-)recent deposits from Russia, Azerbaijan, and Kazakhstan we discuss species discriminations, synonyms, systematic position, as well as uncertainties regarding the type species. Given the apparent loss of all type material, we designate neotypes for all three species. Despite our efforts to collect and analyse new material and available material housed in museum collections, molecular data, and soft-part anatomy are unavailable precluding a firm systematic classification. Overall shell morphology and protoconch microsculpture are indicative of the family Lithoglyphidae. Comparison with Miocene and Pliocene fossils attributed to the genus Zagrabica suggests it to be a likely ancestor of Abeskunus, tracing back the lineage to the late Miocene Lake Pannon. Although the recent literature lists all three species of Abeskunus among the extant Pontocaspian fauna, two of the three species have never been found living and the third one not since the nineteenth century.