Conflicts of interest
=====================

The authors declare that there is no conﬂict of interest.

Introduction
============

The helicarionid land snail genus *Otesiopsis* Habe, 1946 is known from Japan and Taiwan ([@B5428703]). There are five recognised species: *O. japonica* (Möllendorff, 1885), *O. taiwanica* (Kuroda, 1941), *O. kawaguchii* Habe, 1961, *O. kanmuriyamensis* Azuma, 1973 and *O. yamamotoaizoi* Minato, 1974 ([@B5428663], [@B5428693], [@B5364729], [@B5364719], [@B5364748]). While *O. japonica* and *O. taiwanica* have relatively wide distribution areas in western Japan and on the entire island of Taiwan, respectively ([@B5364758]; [@B5364739]), the remaining three species seem to inhabit only limited mountain areas or small islets ([@B5364729]; [@B5364719]; [@B5364748]). The population densities of *Otesiopsis* are considered low (e.g. [@B5364768]). At present, there are only five occurrence records in GBIF (<https://www.gbif.org/species/4599174>). Due to the low population densities and/or restricted distributions, all species except *O. taiwanica* are listed in the national level red data book ([@B5364780]).

Gageodo Island is a small island in South Korea, with an area of about 9.1 km^2^ and situated about 120 km from the Korean peninsula (Fig. [1](#F5364791){ref-type="fig"}). The highest mountain on the island is Mt. Doksilsan with an elevation of 639 m. The non-marine gastropods have so far not been investigated on Gageodo Island.

Materials and Methods
=====================

On 12-14 June 2019, during a field survey, three specimens of the genus *Otesiopsis* were collected on Gageodo Island, Sinan County, South Jeolla Province (Fig. [1](#F5364791){ref-type="fig"}). The shells were examined under a light microscope (Olympus SZ40). The collected specimens were deposited in the Specimen Repository of Kuroha Shell Museum (Voucher No: MNKS3347; 3405; 3476).

Results and Discussion
======================

Order Stylommatophora Schmidt, 1855 (see [@B5428683])

Family Helicarionidae Bourguignat, 1877 (see [@B5428673])

Genus *Otesiopsis* Habe, 1946

*Otesiopsis* sp.

Description
-----------

Shell medium size for this genus, very thin, glossy, dull chestnut brown, with weak growth lines. Whorls 5½ increasing regularly in diameter. Protoconch 1½ whorls with a smooth and glossy surface. Spire moderately low. Suture shallow but distinct. Body whorl with a strong peripheral keel. Base strongly glossy, more convex than the upper part and concave in the umbilical region. Aperture wide, semilunate in outline. Outer lip very thin, sharp, non-reflected, angulated at the periphery, gently curved at the base. Columellar lip short, oblique, slightly thickened. Umbilicus narrowly open.

Height 3.64 mm, width 7.24 mm (Figs [2](#F5364831){ref-type="fig"}, [3](#F5364835){ref-type="fig"}, Voucher No: MNKS3405).

Remarks
-------

Of the three specimens collected in this study, only one individual was sexually mature, which was confirmed by its egg-laying behaviour. Although intraspecific variation needs to be investigated in the *Otesiopsis* snails on Gageodo Island, the adult specimen examined here exhibited distinct differences from other *Otesiopsis* species. The Gageodo *Otesiopsis* has a smaller body size and thicker shell base than *O. japonica* and *O. taiwanica*. It can be distinguished from *O. kawaguchii* and *O. kanmuriyamensis* by having a perforated umbilicus and from *O. yamamotoaizoi* by a larger body size and carinate periphery. *O. yamamotoaizoi* recorded from the Danjo Islands (Nagasaki prefecture, Japan), situated about 380 km southeast of Gageodo Island, is the geographically closest species of *Otesiopsis*.

The *Otesiopsis* snails occurred from Gageodo Island are likely to be an undescribed species. However, morphologies of its reproductive system and radula, which are important traits for classification of *Otesiopsis* (e.g. Habe 1946; Azuma 1973), were not obtained in this study. Further anatomical studies using additional adult specimens are needed to clarify this newly recorded land snail from South Korea. In addition, since the *Otesiopsis* species are generally rare and vulnerable, further field surveys on Gageodo Island and its adjacent areas would be of importance in order to confirm its conservation status.

We express our sincere gratitude to Y. Kim for considerable assistance in the field survey and N. Kawaza for helpful information on Japanese *Otesiopsis*. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1A6A1A05011910). Finally, we are grateful to A. Jochum, T. S. Liew and T. Hirano for providing us with constructive comments on this manuscript.

Conflicts of interest
=====================

The authors declare that there is no conﬂict of interest.

![Sample collection locality in Gageodo Island, South Korea (34°03\'41.2\"N, 125°07\'29.5\"E).](bdj-07-e46984-g001){#F5364791}

![Living individual of *Otesiopsis* collected from Gageodo Island, South Korea. Scale bar = 5.0 mm.](bdj-07-e46984-g002){#F5364831}

![Shell morphology of *Otesiopsis* collected from Gageodo Island, South Korea (Voucher No: MNKS3405). The protoconch was broken. Part of the shell was underexposed. Scale bar = 1.0 mm.](bdj-07-e46984-g003){#F5364835}

[^1]: Academic editor: Alexander M. Weigand
