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 Genus Hemiplecta Albers, 1850 Hemiplecta Albers, 1850: 60, 61. Albers 1860 : 52, 53. Godwin-Austen 1888b : 155-157. Godwin-Austen 1898: 70, 71. Zilch 1959 : 317. Schileyko 2002 : 1282, 1283. Nanina (Hemiplecta) - Adams and Adams 1858 : 222. Nevill 1878 : 46-48. Koratia Godwin-Austen, 1919: 202. Type species: Helix distincta Pfeiffer, 1850, by monotypy. Schileyko 2002 : 1281, 1282. Hemiplecta (Koratia) - Zilch 1959 : 317. Vaught 1989: 97. Ariophanta (Semperia) Godwin-Austen, 1898: 82 [non Crosse 1867 : 74, 75]. Type species. Helix retrorsa Gould, 1843; by original designation. Type species. Helix humphreysiana Lea, 1840; subsequent designation by Martens in Albers (1860) . Diagnosis. Shell dextral or sinistral, medium to large in size (width about 25 to 75 mm) and monochrome to with stripes, or banding patterns. Apertural lip simple to slightly thickened in adult snails; umbilicus open. Genitalia include penial sheath, straight or coiled epiphallic caecum and short flagellum; penial verge may be present or absent. Dart apparatus well developed; gametolytic sac bulbous to elliptical-shaped (without distinct duct). Mantle edge well developed with or without shell lobes. Jaw smooth (without vertical ribs) and crescentic. Radula with unicuspid central teeth, and bicuspid lateral and marginal teeth. Remarks. Due to the high degree of similarity in shell morphology, the specific and generic classification within Ariophantidae is usually problematic. There are at least three nominal genera that are often confused, Nanina Gray, 1834, Ariophanta Des Moulins, 1829 and Cryptozona Moerch , 1872. The genitalia have proved to be the distinguishing characters for specific or generic recognition among the Ariophantidae ( Laidlaw 1932a ; Solem 1966 ; Sutcharit and Panha 2008 ). However, only a few species of each genus have been anatomically examined. Based on this limited anatomical information, the unique characters taken from the type species are summarized in Table 1 . The genus Hemiplecta can be differentiated from these three genera by lacking a gametolytic duct, while the others possess a short to long gametolytic duct. Hemiplecta also differs from Ariophanta and Cryptozona by having unicuspid central teeth, very short or absent flagellum, and a mantle edge with shell lobes; while the latter two genera have tricuspid central teeth, long flagellum, and a mantle edge without shell lobes. In addition, Hemiplecta can be distinguished from Nanina by its short flagellum (Table 1 ). Table 1. Comparison of shell and genitalia characters among four genera of Ariophantidae , mainly based on the characteristics of the type species. The superscript numbers are the references: 1 = Schileyko (2002) , Thiele (1931) , Zilch (1959) , 2 = Blanford and Godwin-Austen (1908) , 3 = Wiegmann (1898) , Sarasin and Sarasin (1899) , 4 = Godwin-Austen (1899), and 5 = Sutcharit et al. (2021) , present study.

Characters	Ariophanta Des Moulins, 18291,2	Nanina Gray, 18341,3	Hemiplecta Albers, 18501,2,5	Cryptozona Moerch , 18721,4
Gametolytic duct	Short	long	absent	short / absent
Gametolytic sac	Bulbous	bulbous	bulbous	bulbous
Epiphallus	short, nearly absent	long	long	long
Epiphallic caecum	long and straight	short and straight	long and straight or coiled	long and straight
Flagellum	very short or absent	long	short	short
Shell lobe	Absent	present	present / absent	absent
Shell coiling	dextral / sinistral	dextral	dextral / sinistral	dextral
Central teeth	Tricuspid	unicuspid	unicuspid / tricuspid	tricuspid
Distribution	South Asia	Indonesia, New Guinea	Southeast Asia, New Guinea	South Asia, Indochina
Type species	Helix laevipes Mueller , 1774	Helix citrina Linnaeus, 1758	Helix humphreysiana Lea, 1840	Helix ligulata Ferussac , 1819

Dextral species in Thailand