Abstract
This study reviews theDicharaxspecies in Thailand. Altogether tenDicharaxspecies are reported, four of which are new to science and described herein. They areDicharax borealisJirapatrasilp & Páll-Gergelysp. nov.,Dicharax burchiJirapatrasilp & Páll-Gergelysp. nov.,Dicharax panhaiJirapatrasilp & Páll-Gergelysp. nov.andDicharax pongratiJirapatrasilp & Tongkerdsp. nov.Alycaeus davisiGodwin-Austen, 1914 is regarded as a junior subjective synonym ofAlycaeus cucullatusTheobald, 1870 (=D. cucullatus) based on a similar depressed-conical shell shape, a long sutural tube and a sharp swelling behind the peristome. Furthermore, the type locality ofAlycaeus pratatensisPanha & Burch, 1997 (=D. pratatensis) had to be amended. Most important characters to distinguishDicharaxspecies are the general shell shape and relative lengths of teleoconch regions, whereas the spiral striation of R1, the shape of swelling of R3, the outer peristome crenulation and protrusion, and the exterior opercular sculpture show large intraspecific variability.
Highlights
Alycaeidae Blanford, 1864 is a family of cyclophoroidean operculate land snails
Several other species have been included in Dicharax in a recent family-wise revision without examining species-level taxonomy (Páll-Gergely et al 2020b)
We report a total of ten Dicharax species from Thailand, six out of ten species being recorded from their type localities only, and the remaining species with additional occurrences within the vicinity of the type locality which ranges wider within Thailand or both Thailand and Myanmar
Summary
The alycaeid shell is characterized by a sutural tube that corresponds with numerous perpendicular microtunnels as described by Páll-Gergely et al (2016) This taxon has been treated as a subfamily of Cyclophoridae by several authors including Bouchet et al (2017), whereas it has been treated as a family of its own by other sources Based on the unique gas exchange system of the shell and the presence of synapomorphic genital anatomical characters, Páll-Gergely et al (2020b) proposed to treat this taxon at the family level, which is followed here. This family ranges from western India to Japan, including Indonesia in the south. This group is known to be diverse in three regions, (1) the southeastern Himalaya, (2) Peninsular
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