Clathrocaspia knipowitschii subsp. knipowitschii knipowitschii (Makarov 1938

Clathrocaspia knipowitschii knipowitschii (Makarov, 1938)

Fig. 13 a–d, f–p

Caspia gmelini [sic] var. Knipowitschii, nov.— Makarov 1938: 1058.

Caspia gmelini [sic] Dyb.— Makarov 1938: 1058, textfig. 1 [non Clessin & W. Dybowski in W. Dybowski, 1887].

P. [yrgula] (Caspia) makarovi sp. n. — Golikov & Starobogatov 1966: 353–354, fig. 1(5).

P. [yrgula] (Caspia) knipowitchi [sic] (Makarov, 1938)— Golikov & Starobogatov 1966: 354, fig. 1(6).

non Pyrgula [(Caspia)] knipowitchi [sic] (Mak.)— Logvinenko & Starobogatov 1969: 379, fig. 367(8).

C. [aspia] knipowitschi [sic] (Makarov, 1938)— Golikov & Starobogatov 1972: 99, pl. 2, fig. 17.

Caspia (Clathrocaspia) knipowitchi [sic] Makarov, 1938 —Anistratenko & Prisjazhnjuk 1992: 19, fig. 2b.

Caspia knipowitchi [sic] Makarov, 1938 — Kantor & Sysoev 2006: 87–88, pl. 41, fig. J.

Caspia makarovi (Golikov et Starobogatov, 1966) — Kantor & Sysoev 2006: 88, pl. 41, fig. L.

Caspia (Clathrocaspia) makarovi (Golikov et Starobogatov, 1966) — Anistratenko 2007b: 796, 797, fig. 2(20).

Caspia knipowitchii [sic] Makarov, 1938 — Anistratenko 2013: 53–55, figs 1A–I, 3A–D, 5A–D.

Caspia makarovi (Golikov & Starobogatov, 1966) — Anistratenko 2013: 56–59, figs 2A–E, 3E.

? Caspia milae n. sp. —Boeters, Gl̂er & Georgiev in Boeters et al. 2015: 180–183, figs 9–21.

Clathrocaspia knipowitschii (Makarov, 1938) — Wesselingh et al. 2019: 70–71.

? Clathrocaspia milae (Boeters, Gl̂er & Georgiev, 2015)— Wesselingh et al. 2019: 72.

Type material. The types of C. knipowitschii are lost. All material of Makarov that was supposedly stored in Odessa was almost certainly destroyed during World War II (M. Son and I. Sinegub, pers. comm. 05/2020); despite considerable effort, the material could not be located in any collection. To fix the identity of C. knipowitschii we designate a neotype. Unfortunately, there is no topotypic material from the mouth of Dniester River in any collection we are aware of, and no fresh material was encountered there during an expedition in 2016. Thus, we choose as neotype a specimen from the nearest possible location with similar ecological settings, i.e. the mouth of the Dnieper River near Kherson, from where Makarov (1938) also reported specimens. The neotype (IZAN 522/1) fits well to the original description in terms of size, shape and sculpture.

The type material of C. makarovi includes the holotype (ZIN 4492 /1), collected by S.A. Zernov in 23/09/1908 (during the “ Academician Baer ” steamship expedition), and 126 paratypes (ZIN 4499 /2–4501/10), collected by S.A. Zernov in 15/08–15/09/1909 (during the “ Meotida ” steamship expedition).

Type locality. The neotype comes from the mouth of Dnieper River near Kherson, Kherson region (Ukraine) (Table 1, locality 30b). The original (lost) type series comes from the mouth of Dniester River. The type locality of C. makarovi is the Dnieper River liman (locality 31).

Other material. Fifty two specimens from the neotype locality (IZAN 522, locality 30b) and three specimens from the close-by locality 30c (UGSB 25234–25236). Further 19 specimens were retrieved from Holocene deposits of near Kiliya, Odessa region, Ukraine (IZAN unnumbered, locality 32); this also includes four paratypes of C. brotzkajae from the same lot referred to C. knipowitschii herein. 228 specimens derive from late Holocene deposits from six piston cores in the Razim-Sinoe lake complex, Romania (RGM 1309843 and unnumbered; localities 33a–f).

Remarks. Detailed descriptions of Clathrocaspia knipowitschii and C. makarovi were provided by Anistratenko (2013), including information on protoconch, radula and operculum. Here we review all material presently available for both species, including the holotype of C. makarovi. Both species comprise a wide range of shell variability, concerning size, shape (elongate versus more bulky) and whorl convexity. Although typical C. knipowitschii sensu Makarov (1938) (Fig. 13a, b) and C. makarovi sensu Golikov & Starobogatov (1966) (Fig. 13c, d, f) can be clearly distinguished, there are numerous intermediate morphologies that do not allow establishing clear species boundaries. Moreover, the different forms co-occur in the same habitats.

Only the protoconch of C. makarovi is slightly smaller than that of C. knipowitschii (Anistratenko 2013) though this feature is also slightly variable. Given the morphological similarity these differences may be considered as intraspecific variation. Moreover, unpublished genetic data suggest that recent populations of Clathrocaspia inhabiting the Dnieper-Bug estuary and determined as C. makarovi and C. knipowitschii belong to a single species (T. Wilke, pers. comm. 05/2020). Hence, we confirm the previous assumption of Wesselingh et al. (2019) and consider C. makarovi as a junior synonym of C. knipowitschii.

As already discussed by Wesselingh et al. (2019), Clathrocaspia milae closely resembles C. knipowitschii. Boeters et al. (2015) distinguished the two species based on the degree of cover of the umbilicus, the shape of the peristome and the size and number of whorls of the protoconch. Most of these characteristics are found to be quite variable within populations of C. knipowitschii. Until molecular information is available we only tentatively list C. milae among the synonyms of C. knipowitschii. Moreover, while soft-body morphology of C. milae was described by Boeters et al. (2015), data on the anatomy of C. knipowitschii are not yet available.

The concept of C. knipowitschii applied in the literature differs largely among authors. For example, C. knipowitschii sensu Logvinenko & Starobogatov (1969), who list the species among the Caspian Sea gastropods, is much broader than “real” C. knipowitschii; their illustration closely resembles C. brotzkajae, and we consider their record synonymous with that species (see also Remarks section of that species).

Distribution and ecology (including C. makarovi). Restricted to the Azov-Black Sea Basin, where the species occurs in Taganrog bay, delta of the Don, Dnieper, Dniester, Danube rivers, estuaries and coastal lakes of NW part of the Black Sea Basin (Golikov & Starobogatov 1972; Anistratenko 2007a; our data). Also known from Holocene deposits of the Danube Delta (Anistratenko & Prisjazhnjuk 1992) and offshore Crimea (in phaseoline silt; Golikov & Starobogatov 1966, 1972).

In the Dnieper-Bug estuary, C. knipowitschii inhabits lotic waters of the Dnieper riverbed and its branches usually at a depth of 2– 10 m. In 2015, a maximal population density of 4590 spec./m² and a and biomass of 7.73 g /m² were measured in the Dnieper across from Kherson Hydrobiological Station on silty sand among the colonies of Dreissena at a depth of 2 m (Alexenko & Kucheryava 2019, T. Alexenko, pers. comm. 06/2020). Snails prefer substrates such as sand, silty sand, as well as the shells or shell fragments of bivalves and gastropods; in some localities in the Southern Bug snails occurred on stones at 1 m depth (Alexenko & Alexandrova 1987; Alexenko & Kucheryava 2019).