Genus Bensonella Pilsbry and Vanatta, 1900

Bifidaria (Bensonella) Pilsbry and Vanatta 1900: 591.

Boysidia (Bensonella) – Pilsbry 1917 (in Pilsbry 1916 –1918): 198.

Boysidia (Paraboysidia) Pilsbry, 1917 (in Pilsbry 1916 –1918): 174, 201.

Type species

Pupa plicidens Benson, 1849 (Fig. 3 (a–e) herein), by original designation.

Remarks

According to Pilsbry̾s (1917) original description of Paraboysidia, this genus (at that time a subgenus of Boysidia) differs from Bensonella by having normal (not hooked) apertural barriers. However, this claim is incorrect because the type species of Bensonella (Pupa plicidens) has normal barriers. The type species of Paraboysidia (Boysidia paviei Bavay and Dautzenberg, 1912, fig. 3(f–k)) is very similar to that of Bensonella (Pupa plicidens) in general shell shell and aperture shape, and in the arrangement of the apertural barriers. The main difference is the presence of some additional ̍supplementary̾ apertural folds (i.e. tiny plicae between main plicae) in P. plicidens, which does not seem to justify the distinction of two genera. Therefore, herein Paraboysidia is treated as a junior synonym of Bensonella. Gittenberger et al. (2021) also treated Paraboysidia as a synonym of Bensonella but did not explain their decision to do so.

Bensonella species with hooked and normal barriers in the Himalaya (i.e. B. hooki sp. nov. and B. plicidens) are very similar to each other in all other shell characters. Moreover, hooked and normal apertural barriers are characteristic of otherwise extremely similar and close-occurring species in the genera Acinolaemus F.G. Thompson and Upatham 1997; Anauchen Pilsbry, 1917; and Hypselostoma Benson, 1856 (Vermeulen et al. 2007, 2019). This suggests that the hooked or normal apertural barriers are subjects of rapid, probably adaptive (see Wada and Chiba 2013) evolutionary changes. Since it is probable that the hooked apertural barriers have been evolved multiple times in different groups within the Hypselostomatidae, it is unlikely that species with apertural barriers would form a monophyletic unit. Therefore, it is not recommended to use this character state to distinguish between genera. We thus classify species with both hooked (B. hooki sp. nov., B. lakainguta Hwang, 2014) and normal apertural barriers (i.e. B. plicidens) in Bensonella.

In the last three decades, several Boysidia (Bensonella) species from China have been newly described or transferred into the (sub)genus: Boysidia dilamellaris D.-N. Chen, Y.-H. Liu and W.-X. Wu, 1995 (transferred to Bensonella by Chen et al. 1999); Boysidia (Bensonella) jinpingensis M. Tian, B. Fao and Y.-X. Chen, 2015; Boysidia (Bensonella) nanjiangensis Z.-L. Zhang, W.-H. Zhang and T.-C. Luo, 2011; Boysidia (Bensonella) qingliangfengensis F. Fang, J. Wang and Y. Chen, 2015; Boysidia (Bensonella) shilinensis D.-N. Chen, M. Wu and G.-Q. Zhang, 1999; Boysidia (Bensonella) tianxingqiaoensis T.-C. Luo, D.-N. Chen and G.-Q. Zhang, 2000 (Luo et al. 2000); Boysidia (Bensonella) tongguanensis D.-N. Chen and W.-H. Zhang, 2002; Boysidia (Bensonella) xingyinensis Y.-H. Guo, W.-C. Zhou and T.-C. Luo, 2006 (Guo et al. 2006); and Boysidia (Bensonella) xiuwenensis W.-H. Zhang, T.-C. Luo and W.-C. Zhou, 2010.

Of these, B. dilamellaris, B. nanjiangensis, B. shilinensis, B. tongguanensis and B. xiuwenensis were classified as within Boysidia Ancey, 1881 (without subgeneric classification) by Zhang et al. (2014). We agree with this classification because these species are similar in shell shape and apertural dentition (i.e. fused angular and palatal lamella) to the type species, Pupa dorsata Ancey, 1881. We further classify B. jinpingensis in Boysidia for the same reason (i.e. that species is a member of Boysidia and not Bensonella). Boysidia (Bensonella) tianxingqiaoensis (treated as a Boysidia species by Zhang et al. 2014) and Boysidia (Bensonella) xingyinensis are here both transferred to Gyliotrachela Tomlin, 1930 due to the free and keeled last whorl and the separate parietal and angular lamella all being similar to those of the type species of that genus: Hypselostoma hungerfordianum Möllendorff, 1891.

Boysidia (Boysidia) fengxianensis D.-N. Chen, Y.-H. Liu and W.-X. Wu, 1995 was transferred to Bensonella by Schileyko (1998) and to Boysidia (Bensonella) by Zhang et al. (2014). Judging as best we can from the poor-quality drawing in the original description (mostly the three parietal lamellae), we agree that this species belongs to Bensonella.

Lastly, the Sumatran Bensonella karoensis Maassen, 1999 is retained in Bensonella herein, due to the arrangement of the apertural barriers (separate angular and parietal lamella, two palatal lamellae, a basal and a columellar lamella) that largely match with the situation in Pupa plicidens Benson, 1849 and Boysidia paviei Bavay and Dautzenberg, 1912, the type species of Bensonella and Paraboysidia, respectively.