Atopos Simroth, 1891

Mitchueachart, Bowornluk, , Chirasak Sutcharit, Panha, & Somsak, 2025, The slug genusAtopos Simroth, 1891 (Systellommatophora: Rathouisiidae) from Myanmar with description of a new species, Raffles Bulletin of Zoology 73, pp. 43-53 : 44-45

Genus Atopos Simroth, 1891

Atopos Simroth, 1891: 596 , 597; Sarasin & Sarasin, 1899: 104–106; Collinge, 1902: 84–87; Heynemann, 1906: 37–38; Ghosh, 1912: 182; Ghosh, 1914: 111–113; Thiele, 1931: 489; Schilthuizen & Liew, 2008: 293, 294; Manganelli et al., 2023: 91–94.

Type species. Atopos semperi Simroth, 1891 by subsequent designation in Thiele (1931: 489).

Diagnosis. The animal has an isosceles triangle cross-section and a short base (formed by the foot). Mid-dorsal region with more or less prominent mid-dorsal keel. Anterior body (about ⅓ of total length) thickest, gradually tapering to posterior end. Head with two pairs of tentacles: upper pair contractile and with dark eye spot on tip; lower pair short and bifid. Genitalia ditrematous: male pore opened behind right lower tentacle; female pore located near anal pore and pulmonary orifice in right pedal groove.

Remarks. Although Simroth gland(s) have been reported in Atopos , there have been no studies or direct observations, so its function is still being studied. However, Laidlaw (1940) and Barker (2001) hypothesised that it probably has a role in the copulatory process because it connects to the male genital organ and is close to the genital opening.

At present, the genus Atopos comprises approximately 30 nominal species. They have a broad distribution, mainly being found in Southeast Asia, but have also been documented in Australia, Papua New Guinea, and India ( Souleyet, 1852; Heynemann, 1876; Simroth, 1891, 1914, 1920; Sarasin & Sarasin, 1899; Babor, 1900; Collinge, 1902, 1903, 1908; Ghosh, 1912, 1913, 1915; De Wilde, 1984; Tan & Chan, 2009; Vermeulen & Liew, 2022).

In Myanmar, A. gravelyi was the first and only species discovered in Kayin State ( Ghosh, 1915) . From this study, we identified one new species, named here as A. transversus , new species, from Shan State, and also documented a new record of A. laidlawi Collinge, 1902 from Tanintharyi Region.