Turricaspia? spica (Eichwald, 1855)

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

Turricaspia? spica (Eichwald, 1855) Fig. 15A-R

Turricaspia spica ? *1855 Paludina spica m.; Eichwald: 303-304, pl. 10, figs 8-9.

Turricaspia spica ? 1887 Micromelania spica Eichw. sp. - W. Dybowski: 29-31.

Turricaspia spica ? 1888 Micr. [omelania] spica Eichw. sp. - W. Dybowski: 78, pl. 1, figs 6a-c, pl. 3, figs 11a-d.

Turricaspia spica ? 1917 Micromelania (Turricaspia) spica Eichw. - B. Dybowski & Grochmalicki: 16-17, pl. 3, figs 22-27.

Turricaspia spica ? 1952 Micromelania spica (Eichwald, 1855). - Zhadin: 252-253, fig. 194.

Turricaspia spica ? 1992 Turricaspia spica . - Anistratenko & Prisyazhniuk: 19, fig. 2d.

Turricaspia spica ? 2006 Turricaspia spica (Eichwald, 1855). - Kantor & Sysoev: 110, pl. 49, fig. F.

Turricaspia spica ? 2009 Turricaspia cf. spica (Eichwald, 1855). - Filippov & Riedel: 70, 72, 74, 76, figs 4e-f.

Turricaspia spica ? 2016 Turricaspia spica (Eichwald, 1855). - Vinarski & Kantor: 250.

Material.

1420 specimens ( RGM 1309784 , RGM 1309785 , RGM 1309786 , RGM 1309811 , RGM 1309812 , RGM 1309813 , RGM 1310229 -1310231, RGM 1310233 -1310237, RGM 1310239 , RGM 1310240 , LV 201501 , LV 201502 ) .

Type material.

Not traced, most probably in ZIN ( Vinarski and Kantor 2016).

Type locality.

"Im kapischen Meere, am Ufer der Insel Tschetschnja, vorzüglich nLittorinimorphastwärs von der Insel im Meeresgrunde" (in the Caspian Sea, at the shores of Ostrov Chechen’, especially on the seafloor northeast of the island).

Dimensions.

6.40 × 2.18 mm ( RGM 1310237, Fig. 15A-C ); 5.93 × 2.27 mm ( LV 201501, Fig. 15D-F ); 6.13 × 2.19 mm ( LV 201502, Fig. 15G-I ); 6.36 × 2.21 mm ( RGM 1310230, Fig. 15J-L ); 6.01 × 1.90 mm ( RGM 1310231, Fig. 15M-O ); 5.88 × 2.00 mm ( RGM 1310233, Fig. 15P ); 5.55 × 1.97 mm ( RGM 1310236, Fig. 15Q ).

Description.

Slender elongate shell, with up to nine convex whorls. Protoconch forms small bulbous cap, consisting of 1.3 whorls that measure 365 µm in diameter; surface weakly granulate, spiral striae set in after 0.5 whorls; nucleus is 140 µm wide; P/T boundary marked by thin, sharp axial line. Early teleoconch whorls have low convex profile. Two morphotypes are present: form A is broader, with whorls increasing slightly more in height (thus producing relatively larger last whorl) and little convex whorls; form B is more slender, whorls increase less fast in height in relation to width and whorl profile is stronger and more regularly convex. Both types are linked via intermediates. Generally, whorl profile varies between regularly convex (of varying strength), laterally flattened or bipartite (with near straight-sided upper half and convex lower half; rarely, transition between halves coincides with spiral thread). Suture is narrow. In some specimens, last whorl is slightly inflated and aperture is expanded. Traces of spiral sculpture, ranging from faint lines to blunt keels of variable number occur on several shells. Aperture expansion and sculpture are found on both morphotypes, as well as in intermediates. Umbilicus mostly covered by inner lip; if open, it is very narrow. Growth lines markedly sigmoidal, with prosocline upper third and opisthocline lower two-thirds.

Discussion.

The huge morphological variability with intergrading morphotypes complicates reasonable taxonomic distinctions within this taxon. Moreover, much of the shape variation (especially in later whorls) seems to be a result of shell repair after predator-induced damage.

The variability also hampers linking our material to an existing name. Several species (and varieties) have been introduced for slender elongate, multi-whorled shells from the Caspian Sea. While the sculptured representatives can be fairly well delimited, the smooth-shelled taxa have caused considerable confusion. Particularly challenging are the many small, slender species with pointy apex, moderately to strongly convex whorls and thin peristome. The group includes (aside from T. spica ): T. elegantula (Clessin & W. Dybowski in W. Dybowski, 1887), T. turricula (B. Dybowski & Grochmalicki, 1915), T. nossovi (Kolesnikov, 1947), T. concinna (Logvinenko & Starobogatov, 1969), T. spasskii (Logvinenko & Starobogatov, 1969), T. uralensis (Logvinenko & Starobogatov, 1969) and T. astrachanica (Pirogov, 1971). Turricaspia lyrata (B. Dybowski & Grochmalicki, 1915), which was originally introduced as subspecies of T. spica , can be well delimited from that group because of its much larger, blunt apex.

A major problem in identifying and discriminating those species is that the concepts applied by later authors occasionally diverge largely from the original perceptions. This especially regards T. spica and the species described by B. Dybowski and Grochmalicki (1915). Unfortunately, the types for these species are not known for sure ( Kantor and Sysoev 2006, Vinarski and Kantor 2016) and the original descriptions, drawings, and illustrations are mostly insufficient to allow distinction. Beyond that, different traits have been considered as diagnostic by different authors when describing new species, and morphological variability was hardly considered at all.

The identity of Turricaspia spica (sensu Eichwald) is dubious. The original description and illustration do not allow distinction from other similar species. The present specimens differ slightly from T. spica sensu Kantor & Sysoev, 2006, which is characterized by a faster whorl accretion rate and relatively higher whorls (including the last whorl). In contrast, our material largely fits the concept of T. spica as used by B. Dybowski and Grochmalicki (1917). We tentatively classify the Selitrennoye specimens in Turricaspia spica , being the oldest available name of the group. Many of the later proposed names might turn out to be junior synonyms. A more in-depth study is required to solve this problematic case.

Distribution.

Turricaspia spica is endemic to the Caspian Sea. After Logvinenko and Starobogatov (1969), it occurs at a water depth between 0 and 30 m, but those authors applied a different concept of the species.

Figures

Figure 15. Pyrgulinae. A-C Turricaspia? spica (Eichwald, 1855), form B, RGM 1310237 D-F T.? spica, transitional form, LV 201501 G-I T.? spica, form B, LV 201502 J-L T.? spica, form A, RGM 1310230 M-O T.? spica, form B, RGM 1310231 P T.? spica, form A, RGM 1310233 Q T.? spica, transitional form, RGM 1310236 R T.? spica, RGM 1309813.