Menestho schikovi Nekhaev 2017, sp. n.

Menestho schikovi Nekhaev sp. n.

Menestho truncatula: Kantor & Sysoev 2006: 243 fig. 122С (partly), non Odhner, 1915.

Type material. holotype (empty shell) (Figs 1A, 2 A, I), 3.12.2015, van Veen grab, ZIN 62135/1, 6 paratypes (empty shells) from the same sample ZIN 62136/2 and 2 paratypes (empty shells) from the same sample LMBI IN- 3.

Type locality. Svalbard, Spitsbergen Island, Billefjorden, R / V Dalnie Zelentsy, sta. 44, 78°39.6'N, 16°40.4'E, 188 m.

Other examined material: 3 spms, 2 shells, Kara Sea, 76°41'N, 88°14'E, 45 m, R/V G. Sedov, leg. Vagin, 0 6.09.1934, ZIN 22732 (studied with SEM); 4 spms, Kara Sea, 75°40'N, 80°26'E, 42 m, R/V G. Sedov, leg. Vagin, 0 9.09.1934, ZIN 35691; 3 spms, Kara Sea, 76°17'N, 75°08'E, 75 m, R/V G. Sedov, leg. Vagin, 21.09.1934, ZIN 35693; 1 spm, Severnaya Zemlya, 80°30'N, 90°03’E, 174 m, R/V Fyodor Litke, 29.09.1948, ZIN 35701; 1 spm,Laptev Sea, 77°25'N, 115°48'E, 62 m, R/V Sadko, leg. G.P. Gorbunov, 16.08.1937, ZIN 35696; 2 spms, Laptev Sea, 76°36'N, 118°30'E, 51 m, R/V Sadko, leg. G.P. Gorbunov, 0 2.10.1937, ZIN 35697; 1 spm, 71°24'78''N, 174°22'03''E, 585 m, R/V Professor Chromov, 22.08.2004, ZIN 60879.

Diagnosis: Menestho with conical shell, convex, evenly rounded whorls, open umbilicus and straight growth-lines.

Description: Shell small, conical, white or yellowish with convex, evenly rounded whorls divided by deep suture (Figs. 1 A, C, E, 2A). Shell surface with fine, frequent (8–11 on body whorl), spiral ribs, almost semicircular in section, divided by very narrow interspaces (Fig. 2I). Axial sculpture, except for straight growth-lines (Fig. 2A, I) absent. Embryonic shell intorted, of type B, partially eroded on studied specimens, smooth or with very low pattern of spiral sculpture (Fig. 2G). Aperture oval with acute angle in upper part, no teeth or folds on columella. Umbilicus clearly visible, narrow. Operculum transparent, without peg (Fig. 2E).

Measurements of holotype: shell height = 3.6 mm, aperture height = 1.2 mm, last whorl height = 2.3 mm, shell width = 2.0 mm, aperture width = 1.0 mm.

Variability. Studied shells differ in width/height proportions (Fig 1 A, C, E), no other significant variability had been found.

Distribution. Known from the Svalbard, the Kara and the Laptev seas. Single young specimen (ZIN 60879) with shell height = 2.5 mm corresponded to Menestho schikovi was found from the Chukchi Sea. Depth range 42– 585 m. Probably, the species lives in all seas of the Eurasian Arctic.

Habitat. The species had been collected from silt substrates. The observed near-bottom temperature and salinity at the type locality were -1.4°C and 34.8 psu respectively. Menestho schikovi probably have a parasitic mode of life, like other pyramidellid species. However its host is unknown.

Derivation of name. The species is named after Dr. Evgenij Schikov, enthusiastic malacologist and ecologist.

Remarks. Shell of Menestho truncatula (Figs. 1D, 2B) (see also Odhner (1915) for the figures of syntypes) is wider than M. schikovi, upper part of its last whorl with flattened shoulder, not rounded. The aperture height in M. truncatula is about a half of shell height. In addition, M. truncatula have a reticulate pattern on the protoconch (Fig. 2F). Menestho albula differs from M. schikovi by prosocline growth-lines and absence of an umbilicus. Usually Menestho albula have coarser spiral sculpture and more flattened whorls.

Menestho schikovi very resembles Menestho albula, which was described from West Greenland. However, type material of Turbo albulus had not been found neither during previous studies nor during my own examination of the collections of the Natural History Museum of Denmark, where the collections by Otto Fabricius are stored (Nekhaev et al. 2015). Hence, current knowledge on taxonomic status of Menestho albula is mainly based on topotypic samples collected by H.P.C. Møller (Warén 1991). A single shell from ZIN corresponds with the original description of Turbo albulus in shell shape, size and sculpture as well as with specimens from Iceland studied by Warén (1991) and specimens from the Murman Coast studied in this work. All mollusks have small (3.5 mm in height and lesser) conical, white, shell with flattened whorls (Fig. 1B, 2C–D). The reported size of 9 mm for Menestho albula (e.g. Rosenberg 2009) seems to be a result of confusion with another species. Spiral ribs of Menestho albula are usually of the same width with interspaces (Fig. 2 J–K). Some of the studied specimens from the Murman Coast have a «bend» on the suture (Fig. 2J) whereas others have not. The bend also has not been found in the topotypic specimen (Fig. 2K) and on a shell from Iceland depicted by Warén (1991: Fig. 27F), and hence, with limited knowledge available to date, I suggest that it is an intraspecific variation. All specimens had clearly prosocline growth-lines (Fig. 2 C–D, J–K). The umbilicus of Menestho albula is closed, its embryonic shell is smooth (Fig. 2H). Menestho albula have an Atlantic distribution: the species is known in the waters around Greenland, North of Iceland, Svalbard and SW Barents Sea (Warén 1991; Nekhaev 2014).

Examination of the museum collection revealed that Menestho schikovi had been usually confused with Menestho truncatula. A specimen of the former species was also mistakenly depicted by Kantor & Sysoev (2006) as Menestho truncatula. Examination of museum collections showed that both species occur sympatrically in the Arctic. However, Menestho schikovi had not been found in the Barents and White seas yet. Menestho truncatula seems to be the most common representative of the family in the Arctic and has been found with certainty from Svalbard, all parts of the Barents Sea, the Kara, White, Laptev and East-Siberian Seas (Golikov 1987; Golikov et al. 2001; Nekhaev 2014; Nekhaev & Krol 2017).