Theodoxus wesselinghi Sands & Gloeer sp. nov. Figures 23A-H, 24A-M, 25A-F

Theodoxus fluviatilis: Odabaşı and Arslan 2015: 330-331 (non Nerita fluviatilis Linnaeus, 1758).

Theodoxus anatolicus: Yıldırım et al. 2018: 118 (non Nerita anatolica Récluz, 1841).

Type locality.

Sakarya River, Çayköy, Bilecik, Turkey; 40.0439°N, 30.452°E (Figs 3D, 23A, B).

Holotype. RMNH. MOL.342200 (Sakarya River, Çayköy, Bilecik, Turkey; 40.0439°N, 30.452°E) stored in NMNL: Shell height 6.0 mm, width 6.0 mm (Fig. 24A-D) .

Paratypes. Twenty-four specimens from Sakarya River, Çayköy, Bilecik, Turkey; 40.0439°N, 30.452°E (Fig. 23A, B): 11 in NMNL (RMNH. MOL.342201, RMNH. MOL.342202; Fig. 24E-G) and 13 in UGSB (UGSB 20688, UGSB 20743, UGSB 20744; Fig. 25A, B, D) . Twenty-four specimens from an unnamed roadside spring in Fele, İsparta province, Turkey; 38.00358°N, 31.47217°E (Fig. 23C, D): 11 in NMNL (RMNH. MOL.342203, RMNH. MOL.342204; Fig. 24H-J) and 13 in UGSB (UGSB 20684, UGSB 20735, UGSB 20736) . Twenty-five specimens from Eflatun Pınarı, near Sadıkhacı, Konya, Turkey; 37.8256°N, 31.6748°E (Fig. 23E, F): 11 in NMNL (RMNH. MOL.342205, RMNH. MOL.342206; Fig. 24K-M) and 14 in UGSB (UGSB 20685, UGSB 20737, UGSB 20738; Fig. 25F) . Thirty specimens from Balıkdamı Wetland spring, Eskişehir, Turkey; 39.15277°N, 31.61562°E (Fig. 23G, H): 13 in NMNL (RMNH. MOL.342207) and 17 in UGSB (UGSB 20686, UGSB 20739, UGSB 20740; Fig. 25C, E) .

Etymology.

The species is named in honour of the molluscan palaeontologist Frank P. Wesselingh (Naturalis Biodiversity Center, Leiden, The Netherlands) for his contributions to malacology.

Description.

Shell (Fig. 24A-C, E, F, H-M): Hemispherical, transversely elongate, consisting of typically three whorls that rapidly grow. Spire well defined, moderate height for Theodoxus; often corroded along with other parts of shell. Shell height ranges from 4.0- 6.8 mm, width from 3.8-7.1 mm. Juveniles appear more globular. Periostracum is uniformly ivory or solid black, intermediate forms with broad brown-black smudged diagonal stripes also exist; surface glossy, finely striated with growth lines. Aperture semicircular, no serrations on inner lip. Columellar plate smooth, flat to slightly concave, inclined towards aperture; colouration blue-grey in darker shelled individuals to white in lighter forms.

Operculum (Fig. 24D, G): Operculum plate made of two parts, calcareous base and conchioline lamella; operculum base light, mostly ivory to white, white lamella with distinct orange edge on border with operculum base. Operculum base left adductor can be blunt and rounded, weak callus on top right edge. Apophysis follows same colour scheme as operculum calcareous base, broader at top and narrower and attenuated at bottom. Very narrow rib-shield, deep rib-pouch present on operculum. Operculum lacks a pseudo-apophysis.

Radula (Fig. 25A-F): R-central tooth flanked by A-central, B-central, C-central, E-lateral on each side. Additionally, two interconnected layers of marginal teeth encase central and lateral teeth. R-central shows some variation among populations, slightly spherical or more squared face with slightly concave anterior edge. A-central large and flat with thin ridge that becomes broad and folded right at end of cusp. B-central diminished, forms irregular “S” shape. C-central equally diminished, hidden below lower edge of E-lateral. E-lateral simple with smooth upper edge. First layer of marginal teeth consists of 37-44 teeth that 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.

Based on conchological features of periostracum colouration and patterning and shell shape, it is difficult to differentiate T. wesselinghi sp. nov. from most Asian Theodoxus spp. given the variety in colour and patterns among the type material (Fig. 24A-M). However, in some instances it can be distinguished from Anatolian morphotypes of T. baeticus, which typically displays ivory blotches on a brown background (Fig. 7A-D); T. altenai with clear ivory checks on a dark brown-black background (Fig. 4A-G) and T. gloeri lacking shell pigmentation and bearing strong axial ribs on the shell (Fig. 11A-C). The light ivory-coloured operculum calcareous base makes this species distinct from T. gurur sp. nov. (light to dark brown; Figs 13D, 24D, G) and T. wilkei sp. nov. (bright orange; Figs 24D, G, 27D).

More differentiating features occur in the operculum structure (Fig. 24D, G). The presence of an attenuated apophysis distinguishes T. wesselinghi sp. nov. from T. altenai and T. jordani, which have non-attenuated apophyses (Figs 4, 15, 17). A rib-pouch and rib-shield are either totally lacking or extremely diminished in T. altenai, T. anatolicus, T. jordani, and T. macri (Figs 4, 5, 15, 17, 18), while they are more pronounced in T. wesselinghi sp. nov. (Fig. 24). The rib-shield in T. wesselinghi sp. nov. is however less broad than that typically observed in T. fluviatilis and T. baeticus (Figs 6 - 10). Furthermore, 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, 17, 18). Additionally, the presence of a weak callus on the top right edge of the operculum base in T. wesselinghi sp. nov. helps to differentiate this species from T. gurur sp. nov. and T. jordani, which lack a callus (Figs 13, 15, 17, 18, 24), as well as from T. anatolicus, T. fluviatilis, T. major, T. pallidus, and T. wilkei sp. nov., which have stronger calluses (Figs 5, 9, 10, 19, 20, 24, 27).

Based on the available data for Theodoxus ralulae, T. wesselinghi sp. nov. can be distinguished by a more globular R-central face from T. gurur sp. nov., T. wilkei sp. nov., T. fluviatilis, and T. jordani, where it is more rectangular or triangulate (see Baker 1923; Zettler 2008; Figs 14B, 25B, 28B). Furthermore, the smooth upper edge of the E-lateral can be used to distinguish this species from T. wilkei sp. nov. and T. major, which generally have E-laterals with serrated edges (see Anistratenko et al. 2017; Figs 25C, 28C, D).

Remarks.

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

Distribution.

Known so far only from the four localities in central-west Anatolia (Figs 3D, 23A-H).

Ecology.

Theodoxus wesselinghi sp. nov. can be found in both springs ( Balıkdamı Wetland, Eflatun Pınarı, Fele; Fig. 23C-H) and streams (Sakarya River, Çayköy; Fig. 23A, B) with clear water. The occurrence of macrophytes appears negligible to the species as it occurs in localities both with (Fig. 23E-H) and without (Fig. 23A-D) aquatic plant growth. The floors of all localities are made up of coarse grained sand and large and small rocks and stones that T. wesselinghi sp. nov. is often attached to (personal observation M.E.G.; Fig. 23H). Theodoxus wesselinghi sp. nov. co-occurs with Potamopyrgus antipodarum (Gray, 1843) and Isparta felei Yıldırım, Koca, Gürlek & Glöer, 2018 in Fele spring, Falsipyrgula sp. in Eflatun Pınarı, and Pseudamnicola natolica ( Küster, 1852) (and possibly also T. gloeri; Odabaşı and Arslan 2015) in the Balıkdamı Wetland spring (personal observation M.E.G.).