Lymnaea Lamarck, 1799

Aksenova, Olga V., Vinarski, Maxim V., Itagaki, Tadashi, Ohari, Yuma, Oshida, Tatsuo, Kim, Sang Ki, Lee, Jin Hee, Kondakov, Alexander V., Khrebtova, Irina S., Soboleva, Alena A., Travina, Oksana V., Sokolova, Svetlana E., Palatov, Dmitry M., Bespalaya, Yulia V., Vikhrev, Ilya V., Gofarov, Mikhail Yu. & Bolotov, Ivan N., 2024, Taxonomy and trans-Beringian biogeography of the pond snails (Gastropoda: Lymnaeidae) of East Asia: an integrative view, Zoological Journal of the Linnean Society 201 (4), pp. 1-24 : 13

Genus Lymnaea Lamarck, 1799

Lamarck 1799: 75.

Type species: Helix stagnalis Linnaeus, 1758 (by monotypy).

Diagnosis: Shell large (≤ 70 mm height, usually 40–50 mm), ovate-conical to ear-shaped ( Fig. 3J); both shell size and shell proportions are prone to high variability, both within and among populations. Aperture relatively large, with the body whorl moderately to greatly inflated. Prostate with numerous small folds inside. Praeputium is thick and sac-like, its length exceeds the penis sheath length by 2.5–7.0 times ( Fig. 4F). The latter is very short and narrow. Penial knot is present.

Species richness: Most authors include a single species, the great pond snail, Lymnaea stagnalis , which is thought to be widely distributed in Eurasia and North America [but see Kruglov and Starobogatov (1985a, 1993), who split Ly. stagnalis s.l. into a series of morphospecies, five of them living in North America and six in Eurasia]. Our phylogenetic analysis supports the hypothesis that the great pond snail might be a series of morphologically cryptic species, virtually indistinguishable both conchologically and anatomically ( Aksenova et al. 2023).

Distribution: Holarctic; introduced to some tropical regions of the world. Most of the species belonging to this genus occur in Eurasia, whereas North America is probably inhabited by a single species, Lymnaea jugularis Say, 1817 (= Lymnaea appressa Say, 1821 ) ( Fig. 3I). In the East Asian region, we accept a single species, which is widely distributed throughout the Altai, East Siberia, the extreme northeast of Asia, West China (Xinjiang), and, probably, Mongolia. The oldest available name for this species is Lymnaea sorensis W. Dybowski, 1912 , based on its type locality of Lake Baikal. The type series of this species is housed in the ZIN collection ( Fig. 3J). In addition, we studied numerous topotypic specimens of this species collected in June 2021 ( LMBI collection). Based on these considerations, we adopt this name for the clade of sequences from Northeast and Central Asia. Conchologically and anatomically, it corresponds fully to the great pond snail, which is common in Europe and West Siberia. There are no similar species in East Asia.

Nomenclatural remark: Say (1817a) described Ly. jugularis as a species of ‘great pond snail’ in North America. Some authors accepted this name, treating Ly. appressa as its junior synonym (e.g. Kruglov and Starobogatov 1993). In contrast, Burch (1989) explicitly ignored Ly. jugularis as an available name, without providing an explanation. Clarke (1973: 300–301) argued that Ly. jugularis is unrecognizable because it was based on a very short and incomplete description that was not accompanied by a figure. He characterized this species as ‘a doubtful inhabitant of the United States’. Clarke (1973) decided to use the name Ly. appressa for this species. Later, Clarke (1981) opined that ‘Say’s first (1817) description of jugularis is recognizable’ and that appressa was its junior synonym. The type specimens of Ly. jugularis are lost, which might prevent researchers from reaching an agreement on the identity of this name. In contrast, the type series of Ly. appressa is extant (see Baker 1911: 141) and available to identify this species. To resolve this confusing situation, we here designate a neotype for Lymnaea jugularis Say, 1817 . This specimen was collected from an unknown locality in Minnesota, North America, in the mid-19th century and is kept in ZIN (no. 1 in the systematic catalogue). The exact sampling date is unknown; we know only that this sample was obtained from the United States National Museum in the end of the 19th century ( Fig. 3K). This specimen shows all characters typical for the Nearctic Lymnaea stagnalis s.l. as they were described in papers by Baker (1911), Clarke (1973, 1981), and some other North American authors.