Systematic review of the dextral Hemiplecta Albers, 1850 (Eupulmonata, Ariophantidae) from Thailand with description of a new species and list of all the Indochinese species Author Sutcharit, Chirasak Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand jirasak4@yahoo.com Author Panha, Somsak Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand & Academy of Science, The Royal Society of Thailand, Bangkok 10300, Thailand text ZooKeys 2021 2021-06-28 1047 101 154 http://dx.doi.org/10.3897/zookeys.1047.65735 journal article http://dx.doi.org/10.3897/zookeys.1047.65735 1313-2970-1047-101 12E8706355C44D5F821853F867E27908 199EAC1979F8501BB42D0A51CD52BB67 Hemiplecta esculenta Maassen, 2006 Figures 1F , 5C , 7 , 10H, I Hemiplecta esculenta Maassen, 2006: 17, 18, figs 10-12. Type locality: limestone area near village Hang, Pu Luong National Park, Thanh Hoa, Vietnam. Inkhavilay et al. 2019 : 76, fig. 35d, e. Pall-Gergely 2019 : figs 11-13. Type specimen. See the species list of Indochinese species. Material examined. Thailand : Tam Chiang Dao , Chiang Mai : CUMZ 4553 ( 5 specimens in ethanol; Fig. 1F ), CUMZ 4564 ( 10 specimens in ethanol), CUMZ 4565 ( 9 specimens in ethanol), CUMZ 4574 ( 8 specimens in ethanol; Fig. 5C ); Tam Tab-Tao, Chaiprakarn, Chiang Mai : CUMZ 4580 ( 10 specimens in ethanol) . Shell. Shell relatively small (height up to 25 mm , width up to 35 mm ), elevated to slightly depressed, upper surface with distinct nodules arranged on growth line, and lower shell surface nearly smooth. Last whorl keeled; aperture large and ovate; lip simple to slightly expanded and dark brown. Umbilicus widely opened and deep (Fig. 5C ). Genitalia. Genital tracts similar to those of H. humphreysiana (Fig. 7A ). Internal wall of penis with sculpture encircling penial verge. Penial sculpture (ps) consists of small to large papillary knobs arranged in oblique lines on penial wall; relatively smaller knobs surrounding penial verge. Penial verge (pv) small, short, conic, and with smooth surface (Fig. 7B ). Gametolytic sac (gs) bulbous with undifferentiated duct. Internal wall of vagina with series of thin longitudinal vaginal pilasters (vp). Dart apparatus (da) relatively short; internal wall of chamber with smooth wall, and papilla of dart apparatus (dp) slightly elongate, conic, and with smooth surface (Fig. 7B ). Figure 7. Genitalia, mantle edge structure, and caudal region of Hemiplecta esculenta , specimen CUMZ 4553 from Chiang Mai , Thailand A whole genital organ B internal wall sculpture of penis, vagina and dart chamber C ventral view of mantle edge and D right view of caudal region. Radula. Each row possesses about 161 teeth (80-(18-21)-1-(19-21)-80). Central tooth triangular, tricuspid; ectocones small; mesocone large (Fig. 10H ). Lateral teeth tricuspid; endocone small; mesocone large with pointed tip; ectocone large, basal, and with pointed tip. Outer lateral teeth arranged slightly obliquely, bicuspid; endocone very small to absent; mesocone large trapezoid; ectocone basal, relatively small, and pointed tip. Latero-marginal transition starts from tooth no. 18 to 21. Marginal teeth with curved teeth, bicuspid; endocone usually larger than ectocone (Fig. 10I ). External features. Living snail exhibits similar soft body morphology, pulmonary cavity and caudal structure (Fig. 7D ) to that of H. humphreysiana . The distinct characters are the brownish to greyish body and mantle edge; right and left shell lobes absent (Fig. 1F ). Distribution. Previously known only from the type locality in northern Vietnam ( Maassen 2006 ) and Xieng Khaung, northeastern Laos ( Inkhavilay et al. 2019 ). Recently, we have located populations from northern Thailand in Chiang Mai Province. Remarks. The shell features were carefully described in Maassen (2006) . The original description of H. esculenta was based on seven shells and placement within Hemiplecta was provisional ( Maassen 2006 ), and none of the topotypic specimens have subsequently been examined. The samples from Thailand show only minor variations from the type series, in the presence of a narrow brownish spiral band and slightly elevated spire, which we attribute to intraspecific variation. It is important to examine the genitalia of the topotypic material.