New species of the dancing semislug Cryptosemelus Collinge, 1902 (Eupulmonata, Ariophantidae) from Loei Province, northeastern Thailand with a key to genera of mainland Southeast Asian semislugs and a key to species of the genus Author Tumpeesuwan, Sakboworn Department of Biology, Faculty of Science, Mahasarakham University, Kantharawichai District, Maha Sarakham 44150, Thailand Author Tanmuangpak, Kitti Palaeontological Research and Education Centre, Mahasarakham University, Kantharawichai District, Maha Sarakham 44150, Thailand Author Tumpeesuwan, Chanidaporn Department of Biology, Faculty of Science, Mahasarakham University, Kantharawichai District, Maha Sarakham 44150, Thailand ctumpeesuwan@yahoo.com text ZooKeys 2023 2023-05-19 1163 47 59 http://dx.doi.org/10.3897/zookeys.1163.103650 journal article http://dx.doi.org/10.3897/zookeys.1163.103650 1313-2970-1163-47 2DB90CB6E7464887B71BA5D7D7092CEF 9480EC110E425078B0719BE5F4CDE4F9 Cryptosemelus niger S. Tumpeesuwan & C. Tumpeesuwan sp. nov. Figs 1 , 2 , 3 , 4 Cryptaustenia sp. Tanmuangpak 2016 : 109-110. Cryptaustenia sp. Chimsaeng 2019 : 41-42. Type material. Holotype . NHMSU-00054 (Fig. 3 ). Phu Pha Lom limestone area, Mueang Loei District, Loei Province, northeastern Thailand, coll. Kitti Tanmuangpak, Nov. 2012. Paratypes . NHMSU-00055. Same locality and same date as holotype. Type locality. Phu Pha Lom limestone area, Mueang Loei District, Loei Province, Thailand. Diagnosis. Animal with blackish body, shell lobes with blackish reticulated skin (Figs 2 , 3 ). Genitalia with very short cylindrical vagina, smooth elongated cylindrical epiphallus, without penial caecum (Fig. 4 ). Radula with bicuspid lateral teeth (Fig. 5B, C ). Figure 4. Genital system of Cryptosemelus niger S. Tumpeesuwan & C. Tumpeesuwan, sp. nov. (paratype NHMSU-00055) A photograph and B drawing by Kitti Tanmuangpak. Figure 5. Radula morphology of Cryptosemelus niger S. Tumpeesuwan & C. Tumpeesuwan, sp. nov. (paratype NHMSU-00055) A radula plate, teeth rows arranged in wide V-shape B close-up view of middle part of radula C close-up view of right side of radula D close-up view of right side of radula showing marginal teeth. Central teeth indicated by 'C' ; lateral teeth indicated by 'L' ; marginal teeth indicated by 'M' . Description. (empty shells = 8, living specimen = 4) Shell (Fig. 2A ). Shell globose, small size (shell height 6.03 +/- 0.71.00 mm, shell width 9.72 +/- 1.32 mm), shell imperforate, thin, smooth, dark brown color; transparence, aperture large (aperture height 5.28 +/- 0.68 mm and aperture width 5.71 +/- 0.81 mm). Genital system ( N = 3) (Fig. 4 ). Atrium (at) short. Penis rather long and cylindrical, with thin penial sheath covering entire penis. Penial retractor muscle (prm) present, short, thin and attached at junction of e1 and e2. Epiphallus (e1+e2) length is slightly equal to penis length, surface smooth, e1 cylindrical and gradually smaller in diameter, e2 cylindrical and larger than e1. Flagellum absent. Vas deferens long. Vagina is shorter than penis, cylindrical. Gametolytic duct (gd) thickened at base, gametolytic sac (gs) swollen gland at distal end. Free oviduct (fo) is shorter than vagina. Uterus and prostate gland long and stout. Radula ( N = 3) (Fig. 5 ). Teeth arranged in a wide V-shape with half row formula: 1-7-70+teeth. Central teeth symmetric tricuspid. Lateral teeth and marginal teeth gradually changing from broad to narrow bicuspid. External appearance (Figs 2B , 3 ). Living semislug with reticulated skin, blackish to dark body marked by conspicuous grooves running downward. Four mantle extensions well developed and same color body. Shell lobes do not cover entire shell. Caudal horn absent. Etymology. The species name " niger " is derived from Latin word, meaning "black" referring to blackish body and mantle extensions. Distribution, habitat and behavior observations. Cryptosemelus niger sp. nov. is a species restricted to the dry evergreen forest that covers the Phu Pha Lom limestone area, Loei Province, Thailand. We searched after rain and found the specimens normally hiding on the ground and in the leaf litter. When the snails were disturbed, they escaped by quickly flipping and waging their tail. Information on its natural predators is unknown, but the carnivorous land snails, Discartemon sp., Oophana sp. ( Streptaxidae ), and Sinoennea loeiensis Tanmuangpak & S. Tumpeesuwan, 2015 ( Diapheridae ) were found in the same locality ( Tanmuangpak et al. 2012 ; Tanmuangpak et al. 2015 ; Tanmuangpak 2016 ). Remarks. Cryptosemelus niger sp. nov. differ from other Cryptosemelus species by its black body and mantle lobes. The shell seems to have a more rapidly descending whorl than in C. gracilis and C. betarmon , but is similar to C. tigrinus . Cryptosemelus gracilis also lack a penial caecum but differs in the undulated surface patch on the proximal part of e2. The epiphallus and penis are cylindrical without a caecum, diverticulum, and granulate surface. The radula of the new species differs from all Cryptosemelus in having bicuspid lateral teeth, whereas other species have tricuspid lateral teeth (Table 2 , Figs 2A, B , 3A-D , 4 , 5B-D ). Table 2. Comparison of shell, genital system and radula of Cryptosemelus spp. (data for C. gracilis , C. betarmon and C. tigrinus based on Pholyotha et al. 2021a ).

Characters	C. gracilis	C. betarmon	C. tigrinus	C. niger sp. nov.
Shell :
Shape	Less, globose	Depressed, subglobose	Globose	Globose
Shell width	Up to 6.6 mm	Up to 7.4 mm	Up to 10.7 mm	Up to 11.04 mm
Shell height	Up to 4.2 mm	Up to 4.1 mm	Up to 7.6 mm	Up to 6.74 mm
Whorls number	3 1/2 -4	3 1/2 -4	4-4 1/2	3-4
Shell color	Pale golden amber	Pale yellowish with olive tinge	Pale yellowish with olive tinge	Dark brown transparent
Living snails :
Shell lobes coloration	Monochrome blue-gray to blackish	Monochrome pale to dark-grayish	Pale yellowish-orange banded	Blackish reticulated skin
Radula :
Radula formula	1-(19-20)-38	1-(27-28)-37	1-(38-39)-44	1-7-70+
Central tooth	Tricuspid	Tricuspid	Tricuspid	Tricuspid
Lateral teeth	Tricuspid	Tricuspid	Tricuspid	Bicuspid
Marginal teeth	Tricuspid	Bicuspid	Bicuspid	Bicuspid
Genital system :
Epiphallus e2: Proximal part	Enlarged with irregularly undulated surface patch	Enlarged and with undulated surface	Cylindrical smooth surface	Long cylindrical with smooth surface
Epiphallus e2: Distal part	Smooth surface	Cylindrical and gradually tapering to distal end, smooth surface	Cylindrical with prominently granulated surface	Long cylindrical with smooth surface
Penial caecum	Absent	Present	Present	Absent
Vagina	Larger and shorter than penis length	Smaller and shorter than half of penis length	Long slender and longer than half of penis length	Smaller and shorter than penis length