Aenigmatoconcha sumonthai, a new helicarionid land snail from Chumphon Province, Southern Thailand (Helicarionidae: Durgellinae) Author Tumpeesuwan, Chanidaporn Author Tumpeesuwan, Sakboworn text Raffles Bulletin of Zoology 2018 2018-03-19 66 170 176 journal article 8450 10.5281/zenodo.4504598 5b2d651a-1c6b-445d-b1cc-62eb3ad7e85f 2345-7600 4504598 932CC6CE-9BB3-40CD-B22F-691F70FE5475 Aenigmatoconcha sumonthai , new species Figs. 2–6 ; Table 1 Type material. Holotype : NHMSU-0015 ( Fig. 3 ). Shell height 8.0 mm, shell width 14.2 mm ; type locality: Tham Chang Phueak limestone range, Mueang district , Chumphon province , southern Thailand , coll. Montri Sumontha , May 2015 . Paratypes : NHMSU-0016 (empty shells, genital system and radula, Figs. 4 , 5 ), ZRC .MOL.11287 (one shell), THNHM-Iv-18004 (one shell), same data as holotype . Etymology. The species is named after the collector Montri Sumontha; the specific epithet “ sumonthai ” is from the family name “Sumontha”. Diagnosis. The characters distinguishing Aenigmatoconcha sumonthai , new species , from A. clivicola are the colour patterns on mantle shell lobes and body, as well as morphology of radula and genital organs. Mantle shell lobes bear irregular black marbling pattern and numerous tiny white spots ( Fig. 2A ). Two black bands, each running from the base of a long tentacle (eyestalk) to mantle edge, are present ( Fig. 2A ). Central teeth of radula have a globose unicuspid cusp, with their size smaller than the 1 st lateral teeth and only the distal halves of the globose cusps emerge from the 1 st lateral teeth ( Fig. 4C ). The epiphallus is shorter than penis, and the middle part of the gametolytic sac in the new species is shorter than in A. clivicola ( Fig. 5 ). Fig. 2. Aenigmatoconcha sumonthai , new species , in natural habitat at the type locality; photographs taken on June 2017. A, two snails with the dorsal shell surface complately covered by the mantle shell lobes; B, two snails with mantle shell lobes retracted. (Photograph courtesy of Mr. Montri Sumontha). Description. Shell ( Fig. 3 , Table 1 ): Dextral, flattened to depressed, with a rather wide and deep umbilicus. 6.80–8.00 mm high, 11.50–14.2 mm wide, whorls 4¼–4½, thin, glossy, slightly convex, surface with irregular low axial ridges. Last whorl not descending in front, rounded at periphery. Colour pale brown, glass-like when fresh. Aperture large, ovately lunate, moderately oblique, with a simple and fragile margin, and a short umbilical keel at the umbilical side of the aperture. Fig. 3. External shell morphology; Aenigmatoconcha sumonthai new species , holotype (NHMSU-0015). Body ( Figs. 2 , 6A ; Table 1 ): Living snails possess broad right and left transparent mantle shell lobes, with black marble pattern and numerous tiny white spots. Body pale brown to dark brown, with black bands behind the long tentacles. Foot dark brown, sole tripartite, caudal fossa and caudal horn well developed. Radula ( Fig. 4 , Table 1 ): Rectangle, comprises 22–35 transverse v-shaped rows of teeth and 11–150 teeth in each row. All teeth unicuspid, of spatulate shape. Central teeth are at sharp angles in middle line. Half of cusp body of central teeth emerge from flanking 1 st lateral teeth. Genital system ( Fig. 5 , Table 1 ): Albumen gland of moderate size, slightly swollen. Hermaphroditic duct a rather thick tube. Uterus very long, large, swollen, of dark yellow colour. Vas deferens a long and slender tube, entering apically into epiphallus. Epiphallus a short slender tube, ephiphallic flagellum absent. Ephiphallic retractor caecum shorter and thicker than distal end epiphallus. Penis longer than epiphallus, sausage-shaped. Gametolytic sac comprises three portions, including swollen gland at distal end, slender tube in the middle, and robust tube at base. Vagina yellow in colour, cylindrical, and longer than free oviduct. Free oviduct divided into three parts, distal part short, orange, middle part constricted, and proximal part swollen. Amatorial organ absent. Remarks. Although shell morphology and radula of A. sumonthai are similar to those of A. clivicola , the shell of A. sumonthai is significantly smaller and with less number of whorls ( Table 1 ). The radula of A. sumonthai possesses transverse v-shaped rows of teeth, and the number of teeth in each row is not significantly different from A. clivicola , when the central teeth are excluded. Aenigmatoconcha sumonthai possesses central teeth that have only half of its small globose unicuspid cusp emerging from the 1 st lateral teeth on both sides ( Fig. 4 B–D). Genital systems are notably different, as the epiphallus of A. sumonthai is shorter than penis. The gametolytic sac comprises three parts: swollen gland at distal end, slender tube in the middle, and the base is a robust tube that is longer than the middle part.