Solving the mystery of the misunderstood Bensonella plicidens (Benson, 1849) (Gastropoda: Stylommatophora: Hypselostomatidae)

The Asian land snail species Bensonella plicidens (Benson, 1849) is enigmatic due to its extremely disjunct distribution. That is, it has been reported from the Himalaya, in Eastern China and Japan, and one subspecies was described from Taiwan. This distribution type has not been reported in any other land snails. It is also notable that some specimens identified as B. plicidens have 'normal' plica-like apertural barriers, while others have hook-like projections in the middle of the interrupted barriers, and the hooks point to the outside of the aperture. We examined several Bensonella samples and arrived at the following conclusions: (1) Bensonella plicidens has normal plica-like apertural barriers without hooks, and the Himalayan species with hook-like barriers is a new species, Bensonella hooki Pall-Gergely sp. nov.; (2) the species with hooked barriers recorded from Japan, Taiwan and eastern China differs from both Himalayan species (i.e. Bensonella plicidens and B. hooki sp. nov.), and the name Bensonella lakainguta Hwang, 2014 is available for it; (3) hooked apertural barriers have evolved repeatedly in the Hypselostomatidae and therefore cannot be used as a distinguishing character for the genus Bensonella. Bifidaria (Bensonella) landourensis Pilsbry, 1915 and Boysidia (Bensonella) qingliangfengensis F. Fang, J. Wang and Y. Chen, 2015 are junior synonyms of B. plicidens and B. lakainguta, respectively. Since the type species of Paraboysidia Pilsbry, 1917 and Bensonella Pilsbry and Vanatta, 1900 are very similar in all important shell characters, we consider the former to be a junior synonym of the latter.

Automated summary

The Asian land snail species Bensonella plicidens has a disjunct distribution, with different subspecies having different barrier structures. The species from the Himalaya region and Japan, Taiwan, and eastern China differ from the species in other regions. The barrier structure is not a distinguishing character for the genus Bensonella. Based on the species characteristics and naming rules, the classification of the Bensonella genus has been adjusted.