Radix (Exsertiana) rufescens (Gray in Sowerby, 1822)

Vinarski, Maxim V., Aksenova, Olga V. & Bolotov, Ivan N., 2020, Taxonomic assessment of genetically-delineated species of radicine snails (Mollusca, Gastropoda, Lymnaeidae), Zoosystematics and Evolution 96 (2), pp. 577-608 : 577

9. Radix (Exsertiana) rufescens (Gray in Sowerby, 1822) Figs 4 , G; 6, G-I; Table 1

Lymnaea acuminata Lamarck 1822: 160 (invalid; a junior homonym of Lymnaea acuminata Brogniart, 1810).

Limnaea rufescens Sowerby 1822: 44, pl. 178, fig. 2.

Limnaeus chlamys Benson 1836: 744.

Limnaeus amygdalum Troschel 1837: 168.

Limnaeus nucleus Troschel 1837: 171.

Limnaeus patulus Troschel 1837: 167.

Limnaeus prunum Troschel 1837: 170.

Limnaeus sulcatulus Troschel 1837: 167.

Limnaeus amygdalum - Küster 1862: 35, pl. 6, figs 15, 16.

Limnaea acuminata var. rufescens - Nevill 1877: 27.

Limnaea acuminata - Annandale and Prashad 1919c: 140, pl. V, fig. 1; Germain 1924: 27, figs 23-28.

Limnaea acuminata var. nana Annandale and Prashad 1919c: 141, pl. IV, fig. 1.

Limnaea chlamys - Annandale and Prashad 1919c: 142, pl. V, fig. 3; pl. V, fig. 2.

Limnaea (Pseudosuccinea) acuminata - Annandale and Rao 1925: 177.

Lymnaea auricularia rufescens - Hubendick 1951: 157, fig. 344.

Lymnaea (Pseudosuccinea) acuminata - Subba Rao 1989: 126, figs 254-265, 272.

Radix acuminata - Glöer and Bössneck 2013: 152, figs 52-54, 58-60.

Radix (Exsertiana) rufescens - Aksenova et al. 2018a: 9.

TL.

"The East Indies".

Types.

Probably lost.

The range of this species covers the central part of the tropical Asia; it is known from India, Nepal and Myanmar, but absent from Thailand ( Brandt 1974; Subba Rao 1989; Glöer and Bössneck 2013; Aksenova et al, 2018a).

The shell of R. rufescens is large, its height may approach 45 mm (see Table 1 ). Most probably, it is the largest member of the genus. Hubendick (1951: 56) described its shape in such words: "[shell is] extremely high and slender. Even the body whorl and the aperture are slender". However, this description is fully applicable only to the typical morph of this species. There are varieties with inflated body whorl and not slender aperture (see Fig. 6I ). This high variability allowed some authors to split several intraspecific morphs or even separate species within the R. rufescens s. lato ( Troschel 1837; Annandale and Prashad 1919c; Subba Rao 1989).

Some shells of R. rufescens look almost indistinguishable from shells of certain varieties of R. natalensis (compare Fig. 5E and 5H ). It is problematic to draw a sharp boundary between the two species on the basis of their conchological characters. R. natalensis and R. rubiginosa represent a pair of closely-related vicariant species isolated by the Middle East, where no representatives of Exsertiana occur. Similar to R. natalensis , the relative height of the spire is the most variable shell trait in R. rufescens .

The next three genera discussed ( Ampullaceana , Peregriana and Kamtschaticana ) represent the parts of the former subgenus Peregriana s. lato classified within the genus Lymnaea ( Kruglov and Starobogatov 1993b; Kruglov 2005) or the genus Radix ( Vinarski 2013; Vinarski and Kantor 2016). From the morphological point of view, these three genera cannot be distinguished on the basis of either shell or anatomical characters ( Aksenova et al. 2018a) and they share the same Bauplan of the reproductive system. That is why previous authors considered them as the members of a single subgenus ( Peregriana ; see Kruglov and Starobogatov 1993b; Kruglov 2005) or even lumped them into a single polymorphic species, Lymnaea peregra s. lato (see Hubendick 1951).

Figures

Figure 4. Copulatory apparatuses of the species of the genus Radix. A. Radix auricularia (19.07.2007, Russia, Tyumen' Region, Vylposl channel near Labytnangi Town); B. R. alticola (01.07.2016, Tajikistan, a warm brook near Dzhaushangoz village); C. R. euphratica (04.07.2016, Tajikistan, a roadside ditch near Kurban-Shakhid village); D. R. makhrovi, a paratype (after Aksenova et al. 2018 a, modified). E. R. plicatula (26.11.2014, China, Bejing, an artificial pond in the former Emperor's summer palace). F. R. rubiginosa (Malaysia, Kuala-Lumpur); G. R. rufescens (24.11.2016, Myanmar, Yetho River, near the dam). H. R. natalensis (05.08.2018, Uganda, crater lake Kyamwiga). Scale bars: 2 mm.

Figure 5. Shells of the Central Asian representatives of the genus Radix. A. Radix tener, the type (after Kuester 1862, slightly modified); B. R. persica, the holotype (after Sitnikova et al. 2012); C. R. euphratica (30.08.2013, Russia, Krasnodar Region, Yaseni River, scale bar 2 mm; RMBH); D. R. tenera race euphratica (Iraq, Samara, after Annandale and Prashad 1919 b); E. R. gedrosiana, a syntype (Pakistan, Baluchistan, Quetta, a pond in the Residency garden; after Annandale and Prashad 1919 a); F, G. R. rectilabrum (Pakistan, Northern Baluchistan, Pishin district, Kushdil Khan reservoir; after Annandale and Prashad 1919 a); H. R. iranica, the holotype (from the " Persian Baluchistan "; after Annandale and Prashad 1919 a).

Figure 6. Shells of species of the subgenera Radix s. str. and Exsertiana. A. Radix rubiginosa (Malaysia, Kuala-Lumpur; LMBI); B. R. rubiginosa (1846, Indonesia, Java Island, " Batavia "; ZMUC); C. R. rubiginosa var. intumescens (Indonesia, Java Island, Surabaya; ZMB); D. R. natalensis (= Limnaea undussumae) (Congo, Undussuma; ZMB). E. R. natalensis (= Limnaea arabica Smith; the holotype; NHMUK); F. R. natalensis f. gravieri (10.03.1966, Ethiopia, lower Avash valley, swamp between Assaita and Dubte; NHMUK). G. R. rufescens (24.11.2016, Myanmar, Yetho River, near the dam; LMBI); H. R. rufescens var. patula (India, Ganges River; ZMB); I. R. rufescens var. chlamys (India, Moradabad; probably syntype; NHMUK). Scale bars: 2 mm (A, B, E, F), 5 mm (C, D, G, I).