Theodoxus velox V. Anistratenko in O. Anistratenko et al., 1999

Sands, Arthur F, Gloeer, Peter, Guerlek, Mustafa E, Albrecht, Christian & Neubauer, Thomas A, 2020, A revision of the extant species of Theodoxus (Gastropoda, Neritidae) in Asia, with the description of three new species, Zoosystematics and Evolution 96 (1), pp. 25-66 : 25

Theodoxus velox V. Anistratenko in O. Anistratenko et al., 1999 Figure 22A-M

Theodoxus velox V. Anistratenko in O. Anistratenko et al. 1999: 17-18, fig. 4.7; Wesselingh et al. 2019: 66.

Type locality.

Dnieper Delta, Zburievkiy Liman, Kherson Region, Ukraine.

Type material.

Holotype and five paratypes are stored in IZAN (without coll. no.) .

Remarks.

This species was recently discussed by Wesselingh et al. (2019). While it was previously considered a junior synonym of T. fluviatilis ( Vinarski and Kantor 2016), molecular data shows strong monophyletic support for the independence of T. velox ( Sands et al. 2019a; Fig. 2 ). Nevertheless, T. velox and T. fluviatilis still hold a sister relationship and likely diverged from one another during the early Pleistocene ( Sands et al. 2019a; Fig. 2 ). Theodoxus velox is challenging to distinguish from T. fluviatilis given the overlap in geographic range and similarity of conchological features (Figs 3 , 9 , 10 , 22 ). Theodoxus velox has less phenotypic variability compared to T. fluviatilis (Figs 9 , 10 , 22 ). Moreover, T. velox display more expansive spiral whorls and, in some instances, a more transparent operculum where the conchioline lamella extends deeper into the calcareous base and the callus is less pronounced (Figs 9 , 10 , 22 ).

The geographic distribution range of T. velox overlaps with that of T. sarmaticus (Lindholm, 1901), which has been considered a junior synonym of T. fluviatilis (e.g. Vinarski and Kantor 2016). While T. sarmaticus and T. fluviatilis may on occasion share phenotypic similarity, the morphotypes of T. sarmaticus closely resemble T. velox (Fig. 22A-M versus Fig. 22N-U ). The similarity with T. velox could suggest T. sarmaticus is rather conspecific with that species as suggested by Glöer (2019). Unfortunately, no opercula or soft tissues were preserved among the syntypes of T. sarmaticus to corroborate this hypothesis. Molecular analyses of topotypic material is required to address this uncertainty. However, should this be confirmed at a later point, the name T. sarmaticus would have priority.

Distribution.

This species was indicated to be restricted to drainage systems of the northern Black Sea coast ( Anistratenko et al. 1999; Kantor and Sysoev 2006). Recent molecular data suggest it is distributed as far North as the eastern part of the Baltic Sea and as far South as Anatolia ( Sands et al. 2019a): the only record there derives from Lake Sapanca ( Sands et al. 2019a; Fig. 3C ).

Figures

Figure 2. Dated phylogeny of the genus Theodoxus constructed with BEAST, based on existing GenBank and newly incorporated data for COI, 16 S and ATPα (Suppl. material 1: Table S 1). Morphospecies where associations are queried are highlighted by a question mark after the species name (see the " Systematic checklist " for more information). Small green (PP ≥ 0.95) and red (PP <0.95) dots on nodes indicate the relative posterior probability support of divergence events. Node labels (1 - 32) correspond to divergence dates and HPD intervals in millions of years ago (Mya) for selected nodes (see Suppl. material 1: Table S 3). Dashed dark blue and light blue lines represent the minimum interspecific and maximum intraspecific variation determined by Sands et al. (2019 a) to aid Theodoxus spp. delimitation (see see Methods, Phylogenetics and species delimitation and that study for more information on the delimitation methods).

Figure 3. Occurrence map for Theodoxus spp. in Asia. All points conform to specimens used in the phylogenetic analyses (Suppl. material 1: Table S 1), except for T. gloeri for which no molecular data are available and only the type and paratype localities are indicated. Species are partitioned across four identical maps (A - D) to limit overlap of points as far as possible. Barring T. gloeri, closer related species are grouped together (Fig. 2).

Figure 9. Theodoxus fluviatilis (Linnaeus, 1758). A - D. Specimen collected close to Oued Laabid, Morocco (UGSB 18106) (Fig. 2); E - H. Specimen from the Danube River, Woerth an der Donau, Germany (UGSB 24173); I - L. Specimen (T. euxinus - morphotype) collected in the Papuc Creek, Kiyikoey, Turkey (UGSB 24172) (Fig. 2); M - P. Specimen (T. euxinus - morphotype) from Ovidiopol, Ukraine (UGSB 18124); Q - S. Specimen (T. heldreichi - morphotype) collected in Lake Egirdir, Turkey (UGSB 20361); T, U. Specimen (T. danasteri - morphotype) collected in Krasna Kosa, Ukraine (UGSB 18417) (Fig. 2); V. Opercula of a T. danasteri - morphotype from Lake Skadar, Montenegro (UGSB 24171). Specimens A-D, I-L and T-U were used in the phylogeny (Fig. 2). Scale bars: 1 mm.

Figure 10. Theodoxus fluviatilis (Linnaeus, 1758). A - D. Specimen (conforming to T. sarmaticus) from the Dnieper-Bug estuary, Ukraine (UGSB 18328); E - H. Specimen (T. subthermalis - morphotype) from Novy Afon, Abkhazia, Georgia (UGSB 18402); I - K. Syntype of N. saulcyi from near the Penteli Monastery, Greece (MHNG-MOLL- 111736); L. Specimen (T. saulcyi - morphotype) from Stilos, Crete, Greece (UGSB 20519) incorporated into the phylogeny (Fig. 2). Scale bars: 1 mm.

Figure 22. Theodoxus velox V. Anistratenko in O. Anistratenko et al., 1999. A - D. Specimen from the Dnieper River, Kiev, Ukraine (UGSB 24186); E - H. Specimen collected in the Danube delta, Vylkove, Ukraine (UGSB 24184) used in the phylogeny (Fig. 2); I, J. Holotype from Dnieper Delta, Zbur'ivka Liman, Ukraine (IZAN); K - M. Specimen from Lake Sapanca, Yeni Esme, Turkey (UGSB 20691). Theodoxus sarmaticus (Lindholm, 1901). N - P; Q - S; T - U. Three syntypes from the Oskol River, near Golubino, Russia stored in ZIN (coll. no. 6099 / 24). Scale bars: 1 mm.