Leptogyra bujnitzkii Krol & Nekhaev 2020

Leptogyra bujnitzkii (Gorbunov, 1946)

(Figure 1)

Ganesa bujnitzkii Gorbunov, 1946b: p. 309, pl. 1, fig. 1a–b, v.

Skenea bujnitzkii: Kantor & Sysoev 2006: p. 40, pl. 18D.

Type material. 2 syntypes, R / V Sadko, det. Gorbunov, 24.07.1938, sta. 101, trawl, Zoological Institute of Russian Academy of Sciences No 1908/1.

Type locality. Arctic Ocean, slope of Lomonosov Ridge, 81°50’N, 136°14’E, 3,700–3,800 m.

Diagnosis. Leptogyra Bush, 1897 with skeneiform shell, thin sigmoidal growth lines, wide spiral wrinkles, wide, deep umbilicus. Central tooth of radula wide, rectangular, first three lateral teeth similar, fourth lateral tooth rather large, numerous filamentous marginal teeth.

Description. Shell small (maximal shell width 3.15 mm), skeneiform, light brownish with convex rounded whorls, suture deep, periphery of penultimate whorl rounded, convex. Teleoconch surface with thin numerous sigmoidal growth lines, spiral sculpture consists of wide wrinkles (Fig. 1A, E). Almost whole surface of embryonic shell covered with irregular network sculpture, only narrow part near protoconch border smooth (Fig. 1 C–D). Aperture rhomboid with rounded angles. Umbilicus wide, deep. Periostracum, operculum and soft body unknown. According to original description operculum consist of four whorls in larger specimen, of three whorls in smaller specimen (Gorbunov 1946b).

Radula (Fig. 1 F–G). n -4-1-4- n. Central tooth poorly visible on preparation, wide, rectangular, with thin cutting edge without distinct cusps. Three inner lateral teeth uniform, narrow, with small triangular cutting edge, outer lateral large, with single relatively small triangular cutting edge. Marginal teeth numerous, thin, filamentous.

Measurements of syntype 1: shell height 2.45 mm, body whorl height 2.20 mm, aperture height 1.45 mm, shell width 3.15 mm, aperture width 1.65 mm, diameter of protoconch 308 µm, diameter of the initial part of protoconch 67 µm, number of whorls 3.4, number of protoconch whorls 0.7.

Measurements of syntype 2: shell height 2.30 mm, body whorl height 2.05 mm, aperture height 1.35 mm, shell width 2.95 mm, aperture width 1.50 mm, diameter of protoconch 300 µm, diameter of the initial part of protoconch 67 µm, number of whorls 3.5, number of protoconch whorls 0.7.

Distribution. Known only from the type locality.

Remarks. We suggest that Ganesa bujnitzkii Gorbunov, 1946 actually belongs to the genus Leptogyra. The representatives of this genus have the same pattern of protoconch sculpture, consisting of an irregular network vanishing towards adult whorls (Marshall 1988). The teleoconch sculpture of Leptogyra bujnitzkii resembles that of Leptogyra by the presence of prosocline sigmoidal growth lines and spirally arranged wrinkles or riblets (Bouchet & Warén 1993; Marshall 1988; Warén & Bouchet 2009). The radular morphology of Leptogyra bujnitzkii is the same as in the majority of Leptogyra species (see Marshall 1988).

The irregular network sculpture on the protoconch and the sigmoidal growth lines are also present in Xyleptogyra Marshall, 1988 and Leptogyropsis Marshall, 1988. However, both genera differ from Leptogyra bujnitzkii in radular morphology (Marshall 1988). Leptogyropsis has three curved lateral teeth and a deeply medially split central tooth that is curved laterally. Xyleptogyra has three strongly curved lateral teeth and a wide laterally curved central tooth (Marshall 1988).

Marshall (1988) recognized that Leptogyra constricta Marshall, 1988 and Leptogyra patula Marshall, 1988 have only three lateral teeth. However, he mistakenly interpreted the fourth rather large lateral tooth as innermost marginal. Leptogyra inflata Warén & Bouchet, 1993 has five lateral teeth according to Warén & Bouchet (1993), however, only four laterals can be recognized on the figures provided by these authors. In accordance with Hess et al. (2008), we consider the presence of four lateral teeth as a diagnostic feature of Leptogyra.

Leptogyra bujnitzkii was described in a book presenting results of Soviet studies in the Siberian seas and the Arctic Ocean during the 1930s. The name Ganesa bujnitzkii (like other newly-introduced species names) was first mentioned in the first chapter of this book summarizing ecological, distributional, and biogeographical data for all sea floor fauna known for this region (Gorbunov 1946a). This publication also contains information about the collection site for G. bujnitzkii. However, the morphological description is given in another chapter (Gorbunov 1946b), which constitutes the valid description of this taxon according to the article 13.1 of the International Code of the Zoological Nomenclature.

The coordinates of the type locality given by Gorbunov (1946a) (82°51’ N, 137°23’ E) (Fig. 2B, red star) are different from those on the label of the type lot (81°50’ N, 136°14’ E) (Fig. 2, green star); however, other information, such as depth (3,700 –3,800 m), date of collection (July 24, 1938), and station number (st. 101), is the same in both sources. The sample with Leptogyra bujnitzkii was collected during the forced drift of r/v Sadko, which was blocked by ice together with two ice-breakers, i/b Georgiy Sedov and i/b Malygin (Zubov 1940). The captain of the i/b Georgiy Sedov (Badygin 1950) gives coordinates of the convoy for July 23 and 25, 1938 in his memories (81°50.8’ N, 136°11’ E and 81°51.5’ N, 135°40’ E, respectively), which are very close to the location indicated on the label (Fig. 2C). Therefore, we conclude that they are correctly indicating type locality of this species.

Leptogyra bujnitzkii is the first representative of the gastropod subclass Neomphaliones known from the Arctic Ocean. Representatives of the genus Leptogyra, like other members of the subclass, are known exclusively from habitats such as sunken wood or hydrothermal vents (Hess et al. 2008). Unfortunately, there is no information about the habitat of Leptogyra bujnitzkii. The collection site is located on the way of “transpolar drift stream”: a route of travel of Siberian wood to Greenland and the American continent (Dyke et al. 1997). Bottom communities associated with sunken wood are known from several deep water regions of the extreme North of the Atlantic Ocean, such as from the deep water off Northern Iceland (Warén 1996; Ockelmann & Dinesen 2011) and eastern Greenland (Schulz et al. 2010), but there is no direct evidence about the presence of such biocoenoses from the high Arctic Basin, which remains poorly studied. As there are no known geothermal areas around the type locality of Leptogyra bujnitzkii, we hypothesize that sunken wood is the most probable habitat for this species.

*mean values

**measured from published picture

“-” – no data

based on Marshall 1988, Warén & Bouchet, 1993, 2009 and original data