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

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.

KEYWORDS:

• Non-marine Gastropoda
• endemism
• Pontocaspian biota
• quaternary
• systematics
• Zagrabica

Acknowledgments

Our sincere thanks also go to Diana Delicado, Daniela Esu, Pavel Frolov, Peter Glöer, Mathias Harzhauser, and Dietrich Kadolsky for sharing taxonomic considerations, as well as to Peter Glöer, Katarina Krizmanić, Eike Neubert, Ira Richling, Martina Schenkel, and Tanya Sitnikova for providing information on and/or photographs of type material. We are also grateful to Jan Johan ter Poorten for support during literature research and to Elnara Jafarova and Mustafa Gafarov for their effort to collect new material. This paper contributes to the PRIDE Project (‘Drivers of Pontocaspian Biodiversity Rise and Demise’) funded by the European Union’s Horizon 2020 research and innovation programme. Mathias Harzhauser and two anonymous reviewers are thanked for their constructive comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Data availability statement

Data used for the morphometric analyses and detailed results are available on https://doi.pangaea.de/10.1594/PANGAEA.911223

Additional information

Funding

T.A.N. was supported by an Alexander-von-Humboldt Scholarship, a Martin Fellowship granted by Naturalis Biodiversity Center, and a DFG grant (no. NE 2268/2-1). M.V.V. thanks the Russian Fund for Basic Research for financial support of his taxonomic studies on continental Gastropoda (grant no. 19-04-00270)