Racesina siamensis (G.B. Sowerby II, 1872)

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

25. Racesina siamensis (G.B. Sowerby II, 1872) Figs 8L ; 9K ; Table 3

Limnaea siamensis G.B. Sowerby II 1872: pl. X, fig. 63.

Limnaea luteola f. siamensis - Annandale and Rao 1925: 185, fig. IV(5, 6).

Lymnaea (Radix) luteola - Brandt 1974: 232, pl. 16, fig. 98 (partim).

Cerasina siamensis - Aksenova et al. 2018a: 4.

Racesina siamensis - Vinarski and Bolotov 2018: 332.

TL.

“Siam” (= Thailand).

Types.

Not traced.

Aksenova et al. (2018a) used this name as the oldest one applicable to a species of Racesina which is distributed in Myanmar and Thailand. Though Brandt (1974) considered L. siamensis as a junior synonym of Radix rubiginosa , our data show it is untenable. Despite the substantial genetic distance separating Racesina siamensis and R. luteola , we were not able to find prominent morphological differences between them, either in conchological or in anatomical characters. It allows us to treat R. siamensis as a ‘cryptic’ taxon. Note, however, that we had only a limited number of specimens from Myanmar and some stable morphological differences between the two species will probably be found in future after a thorough study of their intraspecific variation. There is a strong need for a detailed study of genetic diversity and phylogeography of the Racesina luteola species complex.

Morphological note.

In a sample of eleven individuals of R. siamensis from Myanmar, dissected by us, five snails had under-developed copulatory apparatuses or lacked them altogether. No signs of a heavy parasite load were seen, thus the hypothesis of the parasitic castration may be rejected. Such a state (aphally) has been registered in different families of freshwater pulmonates, including Physidae , Planorbidae and Lymnaeidae (see Vinarski and Palatov 2018 and references therein). For the radicines, aphally was reported by Arutyunova (1977). Aphally in aquatic pulmonates is often viewed as an indirect sign of obligate self-fertilisation (autogamy), which may facilitate their introduction into new habitats and rapid establishment of new populations ( Beriozkina and Starobogatov 1991; Jarne et al. 1993). Due to a limited sample size, it is unclear whether our finding indicates that R. siamensis is a species prone to self-fertilisation. However, it is a remarkable fact that the aphally was not found during this research in the rest of the radicine species studied anatomically.

Figures

Figure 8. Copulatory apparatuses of the species in the genera Ampullaceana, Peregriana, Kamtschaticana, Tibetoradix, Racesina, Orientogalba and Bullastra. A. Ampullaceana ampla (11.07.2017, Ukraine, Transcarpathian Region, Irshava River). B. A. balthica (Germany, Mecklenburg-Vorpommern, lake Torgelower See). C. A. dipkunensis (15.09.2016, Ukraine, Transcarpathian Region, Tisa River). D. A. fontinalis (20.08.2017, Russia, Rostov Region, Severskiy Donets River). E. A. lagotis (29.06.2016, Tajikistan, a stream in the Panj River floodplain). F. Peregriana dolgini (13.07.2015, Russia, Tyumen' Region, a floodplain of the Tol'ka oxbow). G. Peregriana peregra (01.07.2006, Russia, Omsk Region, vicinity of Chernoluchye settlement). H. Kamtschaticana kamtschatica (12.04.2014, Russia, Kamchatka Peninsula, Valley of Geysers). I. Tibetoradix hookeri (09 - 10.2012, China, Tibet, a brook, 250 km N of Lhasa). J. T. kozlovi (after Aksyonova et al. 2018 a, modified). K. Racesina oxiana (04.07.2016, Tajikistan, a roadside ditch near Kurban-Shakhid village). L. R. siamensis (24.11.2016, Myanmar, a water reservoir on the Yetho River). M. Ampullaceana relicta relicta (2005, Ohrid Lake). N. Orientogalba ollula (08.07.2010, China, Shaanxi Province, a roadside ditch near Yandi village). O. Bullastra cumingiana (Philippines, Luzon Island, Lake Sampaloc). Scale bars: 1 mm. B - after Schniebs et al. (2011), modified.

Figure 9. Shells of species of the genera Ampullaceana, Kamtschaticana, Myxas, Tibetoradix, Racesina, Orientogalba and Bullastra. A. Ampullaceana relicta relicta (05.1975, Macedonia, a spring near St. Naum monastery, Ohrid Lake region; NHMW). B. A. r. pinteri, a paratype (05.06.1973, Macedonia, Prespa Lake near Perovo; MHMW). C, D. Kamtschaticana kamtschatica (Russia, Kamchatka Peninsula, Valley of Geysers; RMBH). E. Myxas glutinosa (14.09.1963, Kazakhstan, floodplain of the Tobol River near Kustanay City; ZISP). F, G. Tibetoradix hookeri, two syntypes (NHMUK). H. T. kozlovi, the holotype (ZISP). I. Racesina luteola (India, Bengal, Paksay, Pabna; NHMUK). J. R. oxiana (04.07.2016, Tajikistan, a roadside ditch near Kurban-Shakhid village; LMBI). K. R. siamensis (" Thailand "; ZMB). L. Orientogalba viridis, a syntype (Guam Island; NMNH). M. O. ollula (1883, Japan, Yokohama; NHMUK). N. Limnaea bowelli, a type (after Preston 1909). O. Orientogalba cf. bowelli (30.06.1924, China, Tibet, Lingka, 14,500 feet a. s. l.; NHMUK). P. Bullastra cumingiana (Philippine, Cebu Island; NHMUK). Scale bars: 2 mm (C, D, F-H, L, M, O), 5 mm (A, B, E, J-K, N, P).