Invertebrate Zoology, 2020, 17(1): 18–24 © INVERTEBRATE ZOOLOGY, 2020 An Eocene land snail Balticopta gusakovi gen.n., sp.n. (Stylommatophora: Gastrocoptidae) from Baltic amber I.A. Balashov1, E.E. Perkovsky1,2 1 I.I. Schmalhausen Institute of Zoology, B. Khmelnitsky str., 15, Kiev, 01030, Ukraine. 2 A.A. Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya 123, Moscow, 117868 Russia. E-mails: [email protected], [email protected] ABSTRACT: We describe a monotypic genus from Priabonian (late Eocene) Baltic amber that has a moderately small (1.3x2.1 mm), ovate-conic shell with a large free aperture extended to the wall of the penultimate whorl. The parietal margin of the aperture is reflected and has a lip. The aperture is only partially visible because of dirt and an air bubble in the amber. At least one simple angular lamella is present relatively deep in the aperture. How to cite this article: Balashov I.A., Perkovsky E.E. 2020. An Eocene land snail Balticopta gusakovi gen.n., sp.n. (Stylommatophora: Gastrocoptidae) from Baltic amber // Invert. Zool. Vol.17. No.1. P.18–24. doi: 10.15298/invertzool.17.1.02 KEY WORDS: Mollusca, Gastropoda, Pupilloidea, terrestrial molluscs, Priabonian, fossil. Эоценовая улитка Balticopta gusakovi gen.n., sp.n. (Stylommatophora: Gastrocoptidae) из балтийского янтаря И.А. Балашов1, Е.Э. Перковский1,2 1 Институт зоологии им. И. И. Шмальгаузена НАН Украины, ул. Б. Хмельницкого, 15, Киев, 01030, Украина. E-mails: [email protected], [email protected] РЕЗЮМЕ: Описанный новый монотипический род из приабонского (поздний эоцен) балтийского янтаря имеет относительно небольшую (1,3х2,1 мм) овально-коничес- кую раковину с большим свободным устьем, удлиненным на стенку предпоследнего оборота. Париетальный край устья отвернут и имеет губу. Устье только частично видимо в связи с грязью и пузырьком воздуха в янтаре. Имеется, по меньшей мере, один простой ангулярный ламеллярный зуб относительно глубоко в устье. Как цитировать эту статью: Balashov I.A., Perkovsky E.E. 2020. An Eocene land snail Balticopta gusakovi gen.n., sp.n. (Stylommatophora: Gastrocoptidae) from Baltic amber // Invert. Zool. Vol.17. No.1. P.18–24. doi: 10.15298/invertzool.17.1.02 КЛЮЧЕВЫЕ СЛОВА: Mollusca, Gastropoda, Pupilloidea, наземные моллюски, при- абонский. An Eocene land snail Balticopta gusakovi gen.n., sp.n. from Baltic amber 19 Introduction Currently, it is housed in the amber collection of the I.I. Schmalhausen Institute of Zoology, Kiev Terrestrial molluscs are one of the most (SIZK). Syninclusions from the sample have speciose groups of organisms after insects and been removed. apparently have had a similar proportion of Systematics of the family level and higher species since the Cretaceous (Cameron, 2016). follow Bouchet et al. (2017), except that we Although molluscs, in contrast to insects, are believe Orthurethra Pilsbry, 1900 should be very rare in amber. Several snails are known considered a suborder instead of an infraorder, from Cretaceous Lebanese and Burmese amber, and the latter name is more suitable than Pupil- but only two species are described (Roth et al., loidei Schileyko, 1979 (see discussion in Bal- 1996; Yu et al., 2018; Xing et al., 2019). Only ashov, 2016). a few gastropods were reported from Miocene Common terminology for aperture descrip- Dominican amber, without species identifica- tion in Gastrocoptidae is used (e.g. Pilsbry, tion (Poinar, Roth, 1991; Penney, 2010), and 1916–1918; Schileyko, 1998). The term “com- ten snail species have been described from late plete aperture” indicates a continuous peris- Eocene Baltic amber, while only about 20 am- tome: an aperture with all margins, including a ber-embedded snail specimens have been men- parietal margin that can be absent if the walls of tioned in publications (Klebs, 1886; Sandberg- the aperture are connected directly to the wall of er, 1887; Stworzewicz, Pokryszko, 2006, 2015). the penultimate whorl. The term “free aperture” At the same time, at least 3500 arthropod spe- indicates a continuous detached peristome: an cies are known from Baltic amber (Penney, aperture with margins that are not connected to Preziosi, 2014). the wall of the penultimate whorl. The age of Baltic amber was disputed for a long time (e.g., see discussion in Perkovsky et al., 2007), but the Priabonian (late Eocene) Systematics dating of the amberiferous Prussian Formation is strongly supported by available paleontolog- Class Gastropoda Cuvier, 1797 ical data (Aleksandrova, Zaporozhets, 2008). Subclass Heterobranchia Gray, 1840 Extant Holarctic taxa dominate Baltic amber Superorder Eupulmonata Haszprunar et Hu- fauna (Dlussky, Rasnitsyn, 2009; Perkovsky, ber, 1990 2016, 2017; Staniczek et al., 2017); this corre- Order Stylommatophora Schmidt, 1855 sponds well to the Priabonian climate in Russo- Suborder Orthurethra Pilsbry, 1900 Scandia. Thermophilic animals and plants asso- Superfamily Pupilloidea Turton, 1831 ciated with an extant tropical climate are numer- Family Gastrocoptidae Pilsbry, 1918 ous in Ypresian (early Eocene) Oise amber, Ypresian and Lutetian (middle Eocene) com- Genus Balticopta gen.n. pession fossils of Northern and Middle Europe but are much rarer than the aforementioned Type species: Balticopta gusakovi sp.n. Holarctic taxa in Baltic amber and its coeval Diagnosis: Shell ovate-conic, with large free Rovno, Danish and Bitterfeld ambers (Szwedo, aperture extended to the wall of penultimate 2011; Szwedo, Wappler, 2006; Ivanov et al., whorl. Parietal margin of aperture reflected, 2016; Sokolloff et al., 2018 and references with lip. Angular lamella simple, small, not therein). bifurcate, located relatively deep in aperture. Umbilicus small, droplet-shaped. Material and methods Monotypic genus. Etymology: Arbitrary combination of let- The holotype was collected in Yantarnyi ters, -copta from the ending of “Gastrocopta”, (Kaliningrad region, Russia) in 2011 and has the type genus of the family, and “Baltic”, after been stored in V. Gusakov’s private collection. its occurrence in Baltic amber. Feminine. 20 I.A. Balashov, E.E. Perkovsky Fig. 1. Holotype of Balticopta gusakovi sp.n. in amber from three angles. Angular lamella is marked by arrow. Рис. 1. Голотип Balticopta gusakovi sp.n. в янтаре с трех ракурсов. Ангулярная пластинка отмечена стрелкой. An Eocene land snail Balticopta gusakovi gen.n., sp.n. from Baltic amber 21 Balticopta gusakovi sp.n. Etymology: The species is named after Vik- Fig. 1. tor A. Gusakov (Zvyozdny gorodok, Moscow region, Russia), who kindly provided the amber Holotype: SIZK B-13 (original number in piece containing the newly described species. Gusakov’s collection CVGM No. 2MGP2011). The piece of amber is shaped similar to a trian- Discussion gular prism with side lengths of 10 mm, 9 mm and 7 mm, containing a single shell only. Klebs (1886) described two Vertigo species Syninclusions: Diplopoda; Acari; two from Baltic amber, but both are much smaller Diptera, Sciaridae and Cecidomyiidae (Ledomy- (shell widths 0.8 mm and 1.0 mm) than the new ia sp.) (CVGM, N 2 GP2011). species. Thus, they cannot be subadults of the Description: Shell dextral, ovate-conic, with newly described snail. The vertiginid Propupa 4.5 moderately convex whorls. Coloration does hoffeinsorum Stworzewicz et Pokryszko, 2006 not differ from surrounding amber. Shell sur- very different from the new species in shape face almost smooth; very weak irregular stria- (Stworzewicz, Pokryszko, 2006). The recently tion visible on some whorls. Height of body described Ptychalaea mystica Stworzewicz et whorl about half of shell’s height. Aperture free, Pokryszko, 2015 differs from the new species complete, unusually large and extended to the by the incomplete aperture and extremely dif- wall of penultimate whorl forming sinulus in left ferent apertural dentition (Stworzewicz, upper corner (although partial deformation is Pokryszko, 2015). possible), located relatively far forward from One of the most notable features of the new the body whorl; consequently, last whorl before species is its unusual aperture shape. However, aperture relatively elongated forming small curve the shell is damaged, and it is unclear how (partly observable from palatal side, but un- exactly the aperture was naturally constructed. available for imaging because of the angle to the The parietal margin of the aperture may be amber’s surface from this side). Margins of displaced because of damage, but there are no aperture with lip and reflected, including pari- visible deformations on the parietal and palatal etal margin. Inner aperture not easily observ- margins. This lack of visible deformation pro- able due to dirt and air bubble in amber, inner vides evidence that the aperture margins are columellar and basal walls are completely ob- placed at a more or less natural position. Even scured. At least one angular lamellate tooth is when deformation is considered, there are no present (partly visible among dirt on fig. 1, other known species with a reflexed parietal marked by arrow). It is simple, small, not bifur- margin of the aperture developed to this degree cate, located relatively deep in aperture, extend- among similarly shaped genera of Vertiginidae, ed further inside shell (its end inside shell is Gastrocoptidae or any other taxa (Pilsbry, 1916– obscured). Tooth-like structure appears to be 1918, 1920–1921, 1922–1926; Pilsbry, Cooke, present on upper part of palatal wall, but we 1918–1920; Wenz, Zilch, 1959–1960; Gozhik, can’t rule out that this is dirt (visible on fig. 1, Prisyazhnyuk, 1978; Schileyko, 1998; Harzhaus- right from arrow). Other teeth may be present er et al., 2014a, b; Harzhauser, Neubauer, 2018; but unobservable. Umbilicus open, droplet- Nekola et al., 2018). In the new species, the shaped, small, about 0.1 mm width. aperture is elongated and relatively forward Size: Width 1.3 mm, height 2.1 mm, body from the body whorl (“free aperture”), forming whorl’s and aperture’s height 1.1 mm, height of a well-developed parietal margin. visible part of first whorl 0.2 mm, second whorl — The new species is similar to some Vertig- 0.3 mm, third whorl — 0.5 mm.