Systematic revision of the limestone karst-restricted land snail genus Aenigmatoconcha (Eupulmonata: Helicarionidae), with description of a new species Author Pholyotha, Arthit 6CC9B5FE-6586-4132-8289-102DC14D3844 Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. arthitpolyotha@gmail.com Author Sutcharit, Chirasak ED1BD3A8-0B41-4062-A575-EEAC278A9D00 Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. jirasak4@yahoo.com Author Tongkerd, Piyoros 18575FA7-4812-4D75-8568-24D9E7D90BC6 Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. piyorose@hotmail.com Author Panha, Somsak AC935098-D901-4F35-A414-4B0D4FE44E79 Academy of Science, The Royal Society of Thailand, Bangkok 10300, Thailand. somsak.pan@chula.ac.th text European Journal of Taxonomy 2021 2021-09-10 767 55 82 http://dx.doi.org/10.5852/ejt.2021.767.1487 journal article 4208 10.5852/ejt.2021.767.1487 9e3374a3-73e0-4609-a80d-0de905904a37 2118-9773 5528134 A875DB79-C0E1-4C79-A9D0-87CE1464503A Aenigmatoconcha sumonthai Tumpeesuwan & Tumpeesuwan, 2018 Figs 1 , 2C–E , 7A–D , 8 , 10C Aenigmatoconcha sumonthai Tumpeesuwan & Tumpeesuwan, 2018: 171–173 , figs 2–6. Type locality: Tham Chang Phueak limestone range, Mueang District, Chumphon Province , southern Thailand . Material examined THAILAND • 45 sh , 20 sp ; Chumphon Province , Mueang District , Limestone outcrops at Tham Chang Phuek Bureau of Monks ; 10°26′50.0″ N , 99°02′07.1″ E ; CUMZ 7922 • 40 sh ; same collection data as for preceding; CUMZ 7923 • 18 sh , 10 sp ; same collection data as for preceding; CUMZ 7937 • 45 sh , 6 sp ; Chumphon Province , Mueang District , Limestone outcrops at Wat Tham Sanook ; 10°28′51.3″ N , 99°04′28.3″ E ; CUMZ 7924 • 10 sh , 7 sp ; same collection data as for preceding; CUMZ 7925 • 22 sh , 11 sp ; Chumphon Province , Sawi District , Limestone outcrops at Tham Nam Lod Thepnimit Bureau of Monks ; 10°22′39.5″ N , 99°00′39.5″ E ; CUMZ 7927 • 4 sh , 8 sp ; Chumphon Province , Sawi District , Limestone outcrops at Wat Nam Cha ; 10°17′57.0″ N , 99°01′58.5″ E ; CUMZ 7926 . Description SHELL ( Fig. 7A–B ). Shell strongly depressed to depressed, medium-sized (width 14.4–16.6 mm , height 7.0– 8.2 mm ), thin, translucent, whitish colour, well-rounded to slightly shouldered body whorl, elevated spire, impressed suture, obvious varix, and open umbilicus. EXTERNAL FEATURES ( Fig. 2C–E ). Animal with five well-developed mantle lobes. Left and right shell lobes pale yellowish to fleshy-grey colour, usually with black margin, and with or without small to large black spots or blotches. Three dorsal lobes crescent-shaped and smaller than the other two shell lobes. Black stripes behind long tentacles. GENITALIA ( Fig. 8 ). Atrium (at) enlarged and very short. Penis (p) long, cylindrical with thick penial sheath (ps) extending to half of penis length. Inner sculpture of penis with small conical penial pilasters (pp). Epiphallus (e1 + e2) as long as penis: e1 slender, and e2 bulbous. Inner sculpture of e1 with small thin longitudinal folds, while e2 with small papillae arranged in oblique rows. Epiphallic caecum (ec) short with thin penial retractor muscle (prm) attached at tip. Flagellum (fl) small and short. RADULA ( Fig. 10C ). Teeth arranged in anteriorly V-shaped rows with half row consisting of about 63– 65 teeth at the middle plate. All teeth monocuspid and spatulate-shaped with curved cusp. Fig. 7. Shells of Aenigmatoconcha spp. A –D . A. sumonthai Tumpeesuwan & Tumpeesuwan, 2018 . A–B . Specimen CUMZ 7922 from the type locality. C–D . Specimen CUMZ 7937 from the type locality showing the calcareous epiphragm with a small perforation (white arrows). Only shell (C) and living (D) specimens in both lateral and ventral views. E–F . A. eunetis Pholyotha & Panha sp. nov. E . Holotype CUMZ 7931. F . Paratype CUMZ 7933 from Uthai Thani Province. Distribution Aenigmatoconcha sumonthai has a narrow distribution, with populations living on a few limestone hills in Chumphon Province ( Fig. 1 ). We extended our survey, especially among limestone sites about 200 km southwards down to southern peninsular Thailand , but we could not find this species elsewhere. Remarks The lack of a penial sheath and flagellum in the male reproductive organs of A. sumonthai was originally reported to be similar to A. clivicola (Tumpeesuwan & Tumpeesuwan, 2018: 174, fig. 6). In this study, based on topotypic specimens, however, A. sumonthai was found to have a large and thickened penial sheath and small flagellum encircled with loose tissue ( Fig. 8 ). Aenigmatoconcha sumonthai shows variation in the black blotches on both shell lobes ranging from absent ( Fig. 2E ) to the lobes almost entirely covered ( Fig. 2C ). The DNA sequence analysis suggested that these variations formed a clade of A. sumonthai ( Fig. 2 ). In addition, this species develops a calcareous epiphragm with a small perforation to limit body-water evaporation but allowing respiratory gas exchange during dormancy ( Fig. 7C, D ).