Theodoxus wilkei Sands & Gloeer . sp. nov. Figures 26A, B, 27A-J, 28A-F

Type locality.

Çifteler spring, Çifteler, Eskişehir, Turkey; 39.34931°N, 31.05527°E (Figs 3D, 26A, B).

Holotype.

RMNH. MOL.342208 ( Çifteler spring, Çifteler, Eskişehir, Turkey; 39.34931°N, 31.05527°E) stored in NMNL: Shell height 6.9 mm, width 7.5 mm (Fig. 28A-D) .

Paratypes.

Nineteen specimens from Çifteler spring, Çifteler, Eskişehir, Turkey; 39.34931°N, 31.05527°E (Fig. 26A, B): 10 in NMNL (RMNH. MOL.342209-342211; Fig. 27E-J) and 9 in UGSB (UGSB 20687, UGSB 20741, UGSB 20742; Fig. 28A-F) .

Etymology.

The species is named after the molluscan phylogeneticist and evolutionary biologist Thomas Wilke (Justus Liebig University Giessen, Germany).

Description.

Shell (Fig. 27A-C, E-J): Hemispherical, transversely slightly elongate, consisting of typically three whorls that rapidly grow. Spire low, apex often corroded. Shell height ranges from 4.5-7.8 mm, width from 5.2-8.6 mm. Periostracum colour and patterning uniformly ivory or black, intermediate forms black with white-ivory speckles or stripes also exist; surface glossy or dull but always finely striated with growth lines. Aperture semicircular with no serrations on inner lip. Columellar plate is smooth, flat to slightly concave, inclined towards aperture; blue-grey in colour, some yellowing around edges.

Operculum (Fig. 27D): Operculum plate made of two parts, calcareous base and conchioline lamella; operculum base bright yellow to deep orange, darkened orange-brown lamella. Left adductor on operculum base blunt and rounded. Strongly defined callus at top right edge of operculum base. Apophysis light to bright yellow. Apophysis broader at top, narrower at bottom (attenuated). Narrow rib-shield and small rib-pouch present on operculum; pseudo-apophysis lacking.

Radula (Fig. 28A-F): R-central tooth flanked by A-central, B-central, C-central, E-lateral of each side. Additionally, two interconnected layers of marginal teeth encase central and lateral teeth. R-central varies in face shape; can be square face with slightly concave anterior edge or more triangular. A-central large and flat with strong attenuated ridge, broader at cusp. B-central diminished, forms irregular “S” shape. C-central equally diminished, partly hidden below lower edge of E-lateral. E-lateral is simple, semi-smooth to serrate on upper edge. First layer of marginal teeth comprises 37-40 teeth, which decrease in size away from E-lateral but increase in size and bear serrations on edges of small faces; semidetached from second layer, which is fused and forms outer wall.

Differentiating features.

The hemispherical, glossy black, black with white speckles or pure ivory, and finely striated shells of T. wilkei sp. nov. are easily differentiable from T. altenai, which displays light ivory checks on a dark brown-black background (Figs 4A-G, 27A-J), and T. gloeri, which lacks shell pigmentation and bears strong axial ribs on the shell (Figs 11A-C, 27A-J). However, using only conchological features of periostracum colouration and patterning and shell shape, it is still challenging to differentiate T. wilkei sp. nov. from some morphotypes of T. anatolicus, T. baeticus, T. fluviatilis, T. gurur sp. nov., T. jordani, T. macri, T. major, T. pallidus, T. syriacus, T. velox, and T. wesselinghi sp. nov., which can share similar shell shapes and colouration patterning (Figs 5A-M, 6A-G, M, 7M-P, 8A-D, 10E-H, 13A-G, 15P-R, 16C-P, 17A-E, 18A-G, 19O, P, 20A-D, I, J, 21A-D, I-R, 22I, J, 24E-J, 27A-D). Theodoxus wilkei sp. nov. can be distinguished from Anatolian morphotypes of T. baeticus, which typically displays ivory blotches on brown background (Fig. 7A-D); T. jordani, which typically displays brown diagonal zig-zag line patterning on an ivory background (Fig. 15E-L); and T. velox, which has white-ivory stripes on a dark background (Fig. 22K-M). Finally, the bright yellow to deep orange calcareous base of the operculum in T. wilkei sp. nov. can help to distinguish it from T. altenai, T. anatolicus, T. baeticus, T. jordani, T. macri, T. major, T. pallidus, T. syriacus, and T. wesselinghi sp. nov., which typically have lighter calcareous bases ranging from ivory to cream (Figs 4 - 8, 13, 15 - 21, 24); Theodoxus gurur sp. nov., differs in having a light to dark brown operculum (Fig. 13, 27).

There are a number of structural differences on the operculum. The attenuated apophysis in T. wilkei sp. nov. allows a distinction from T. altenai and T. jordani (Figs 4, 15, 17, 27). The presence of a rib-shield and rib-pouch further discriminate T. wilkei sp. nov. from T. altenai, T. anatolicus, T. jordani, and T. macri, where these features are either absent or extremely diminished (Figs 4, 5, 15, 17, 18, 27). Furthermore, the rib-shield in T. fluviatilis and T. baeticus is typically broader than in T. wilkei sp. nov. (Figs 6 - 8, 9, 10, 27). Additionally, the lack of a pseudo-apophysis differentiates the new species from T. altenai, T. anatolicus, T. baeticus, T. gurur sp. nov., T. jordani, and T. macri (Figs 4 - 8, 13, 15 - 18, 27). Furthermore, the more rounded left adductor of the operculum base is only shared with T. syriacus and T. wesselinghi sp. nov. (Figs 21, 24, 27). The strongly defined callus on the top right edge of the operculum base in T. wilkei sp. nov. is only shared with T. anatolicus, T. fluviatilis, T. major, T. pallidus, and T. wilkei sp. nov. and may be used to differentiate this species from all others (Fig. 27D).

Concerning the radula, T. wilkei sp. nov. can be distinguished from T. gurur sp. nov. by a square to triangulate R-central face (Figs 14B, 28B). The serrations on the upper edge of the E-lateral distinguish this species from T. wesselinghi sp. nov., T. fluviatilis, and T. gurur sp. nov., which have smooth, blade-like edges (Figs 14B, C, 27C, 28B-D; also see Zettler 2008).

Remarks.

Theodoxus wilkei sp. nov. forms a part of a larger clade that includes T. syriacus and T. wesselinghi sp. nov., where it shares a closer sister-species relationship with T. wesselinghi sp. nov. (Sands et al. 2019a; Fig. 2). The three species likely diverged from one another within a short time around the Pliocene-Pleistocene transition (Fig. 2).

Distribution.

Only known from the type locality (Figs 3D, 26A, B).

Ecology.

Theodoxus wilkei sp. nov. appears endemic to a freshwater spring environment with clear water (Fig. 26A, B). This spring environment is characterised by macrophytes in the littoral zone and a floor of small and large stones, rocks and course-grained sand (Fig. 26A, B). Theodoxus wilkei sp. nov. is particularly numerous on larger stones and rocks and co-occurs with Pseudamnicola and Melanopsis (personal observation M.E.G.).