Pyrgulinae Brusina, 1882, 1821

Neubauer, Thomas A., Velde, Sabrina van de, Yanina, Tamara & Wesselingh, Frank P., 2018, A late Pleistocene gastropod fauna from the northern Caspian Sea with implications for Pontocaspian gastropod taxonomy, ZooKeys 770, pp. 43-103 : 43

Subfamily Pyrgulinae Brusina, 1882

Pyrgulinae 1882 Pyrgulinae Brusina: 230.

Pyrgulinae 1914 Micromelaniidae B. Dybowski & Grochmalicki: 276.

Pyrgulinae 1915 Turricaspiinae B. Dybowski & Grochmalicki: 103.

Pyrgulinae 2017 Pyrgulinae Brusina, 1882. - Bouchet et al.: 212, 346 [cum syn.].

Discussion.

The Caspian Pyrgulinae (sensu lato) encompasses 64 species that are considered accepted in the current literature ( Vinarski and Kantor 2016). However, most of them are poorly known, documented by insufficient descriptions and drawings; for many, the type material has not been found ( Kantor and Sysoev 2006, Vinarski and Kantor 2016). The extreme morphological variability of several representatives, such as those detected in the material from Selitrennoye, led previous authors to introduce numerous species based on shells with only minor deviations in shape, size or whorl outline. The Caspian Pyrgulinae therefore requires careful revision using molecular and anatomical data as far as available.

In addition to the problems associated with distinguishing species, genus-level classification is poorly resolved as well. Several attempts have been made to categorize this vast variability, and genus concepts have changed tremendously (e.g., B. Dybowski and Grochmalicki 1915, 1917, Zhadin 1952, Logvinenko and Starobogatov 1969, Kantor and Sysoev 2006, Vinarski and Kantor 2016). Twelve genus names have been described for members of the Caspian Pyrgulinae , based on quite different concepts of traits considered diagnostic. Currently, all species are classified within Caspia Clessin & W. Dybowski, 1887, Pyrgula De Cristofori & Jan, 1832 and Turricaspia B. Dybowski & Grochmalicki, 1915 ( Kantor and Sysoev 2006, Vinarski and Kantor 2016). This scheme unites quite a variety of different morphologies under the same genus names, while at the same time similar species are assigned to different genera (e.g., Kantor and Sysoev 2006). Unfortunately, hardly any previous study provided explanations for their genus classifications or systematic concepts in general.

A thorough revision of all Caspian Pyrgulinae is beyond the scope of this study, but we discuss and revise the concepts that have been applied to the species studied herein.

Vinarski and Kantor (2016) listed 38 species of the genus Pyrgula for the Caspian Sea. The type species of Pyrgula De Cristofori & Jan, 1832, P. annulata (Linnaeus, 1758), lives in freshwater lakes and springs in Italy and Dalmatia ( Welter-Schultes 2012). Shell morphology, anatomy and protoconch characteristics are very similar to Pontocaspian Pyrgulinae , e.g., some species of Turricaspia (compare also discussion in Riedel et al. 2001). However, molecular evidence suggests that Pyrgula annulata is only distantly related to the Pontocaspian species flock within the Pyrgulinae , with the last common ancestor dating back to the late Miocene ( Wilke et al. 2007). Therefore, Pontocaspian species should not be attributed to Pyrgula , despite apparent morphological congruence, especially of some of the keeled Pontocaspian Pyrgulinae . A separation on subfamily level as proposed by B. Dybowski and Grochmalicki (1915) is opposed by the latest phylogeny of rissooidean gastropods, which suggests a rather close relationship ( Wilke et al. 2013).

Turricaspia B. Dybowski & Grochmalicki, 1915 (type species: Micromelania turricula B. Dybowski & Grochmalicki, 1915) was introduced for species with turriform, elongate shells with numerous whorls. Presently, the genus includes 22 Caspian species, encompassing elongate and broad, conical and ovoid, and sculptured and smooth species ( Kantor and Sysoev 2006, Vinarski and Kantor 2016). Many species assigned to Pyrgula by Kantor and Sysoev (2006) and Vinarski and Kantor (2016) actually resemble Turricaspia turricula with respect to the turriform, conical shell. This similarity also regards the type species of the genera Caspiopyrgula Logvinenko & Starobogatov, 1969 (type species: Turricaspia nossovi Kolesnikov, 1947), Eurycaspia Logvinenko & Starobogatov, 1969 ( Micromelania pseudodimidiata B. Dybowski & Grochmalicki, 1917), Oxypyrgula Logvinenko & Starobogatov, 1969 ( Pyrgula pseudospica Logvinenko & Starobogatov, 1969), and Trachycaspia B. Dybowski & Grochmalicki, 1917 ( Rissoa dimidiata Eichwald, 1838). After examination of descriptions and illustrations of the type species (e.g., Kantor and Sysoev 2006), we conclude that these genera should be considered as junior synonyms of Turricaspia .

Some of the species classified as Turricaspia by Kantor and Sysoev (2006) and Vinarski and Kantor (2016) differ considerably from Turricaspia s.s. in shell shape. This contains the type species of the genera Caspiella Thiele, 1928 ( Rissoa conus Eichwald, 1838), Clessiniola Lindholm, 1924 ( Paludina variabilis Eichwald, 1838), and Laevicaspia B. Dybowski & Grochmalicki, 1917 ( Rissoa caspia Eichwald, 1838). In turn, some species presently attributed to the genus Euxinipyrgula Sitnikova & Starobogatov, 1999 (type species: Pyrgula milachevitchi Golikov & Starobogatov, 1966) closely resemble species of the Laevicaspia - Caspiella group (compare Anistratenko et al. 2011).

Based on a review of the Pontocaspian species formerly attributed to these genera and illustrated in the literature ( Golikov and Starobogatov 1966, Logvinenko and Starobogatov 1969, Alexenko and Starobogatov 1987, Kantor and Sysoev 2006, Anistratenko 2008), we propose to distinguish the genera Clessiniola and Laevicaspia from Turricaspia , and to treat Caspiella and Euxinipyrgula as junior synonyms of Laevicaspia .

Clessiniola species can be easily distinguished from species attributed to other genera based on their broad shells with a large body whorl and aperture. The situation for the Laevicaspia - Caspiella - Euxinipyrgula is more difficult. The three type species (see above) share the ovoid shape with cyrtoconoid spire, the high whorl accretion rate, the shape, inclination, lateral sinuation and thickening of the aperture, and the extent and sculpture of the protoconch (e.g., Kantor and Sysoev 2006, Anistratenko 2008, and this study). The only differences are shell size and whorl convexity, which we do not consider sufficient to distinguish genera. The adapical thickening of the aperture resulting from downward growing of the shell in late ontogeny as stated in the diagnosis of the genus Euxinipyrgula by Sitnikova and Starobogatov (1999) is also shown for species that have been attributed to Caspiella (see below). The features of the soft-part anatomy considered diagnostic by these authors need to be rechecked and compared to live material from the Caspian Sea to reevaluate the position of Euxinipyrgula . Sitnikova and Starobogatov (1999) also discussed the similarities between Caspiella and Euxinipyrgula , concluding that Caspiella should perhaps be included in the genus Euxinipyrgula , possibly as a separate subgenus (which would be nomenclaturally invalid however).

The ovoid shape, lateral sinuation and thickening of the aperture typical for the Laevicaspia - Caspiella - Euxinipyrgula group are also found among species of the genus Prososthenia Neumayr, 1969 from the middle Miocene of the Dinaride Lake System (e.g., Neubauer et al. 2016b). These species, however, differ in the granulate protoconch making up less than one whorl.

Species of Turricaspia differ from Laevicaspia in the slower, regular whorl accretion, producing a conical spire and a higher number of whorls at the same size. In addition, Turricaspia species have usually more fragile shells, thinner peristomes and often more strongly sinuate growth lines.

The genus Caspia is listed among Pyrgulinae in latest catalogues ( Kantor and Sysoev 2006, Vinarski and Kantor 2016), but it has been shown to be unrelated to that subfamily ( Anistratenko 2013, Bouchet et al. 2017; see discussion of the Caspiinae above).

Finally, several Pontocaspian Pyrgulinae have been previously assigned to the genus Micromelania Brusina, 1874 (e.g., W. Dybowski 1887, B. Dybowski and Grochmalicki 1917). Its type species, Micromelania cerithiopsis Brusina, 1874 (subsequent designation by Dollfus 1912), derives from late Miocene deposits of Lake Pannon. It differs considerably from Pontocaspian Pyrgulinae regarding the presence of 2-4 noded keels and the small size (4.5 × 1.33 mm after Brusina 1874) compared to the rather high number of eight whorls.