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 clivicola Tumpeesuwan & Tumpeesuwan, 2017 Figs 1 , 2A , 4A–B , 5 , 10A Aenigmatoconcha clivicola Tumpeesuwan & Tumpeesuwan, 2017: 184–187 , figs 2–5. Type locality: Phu Pha Lom Limestone Hill in Mueang District, Loei Province , northeastern Thailand . Aenigmatoconcha clivicola – Tumpeesuwan & Tumpeesuwan 2018: 171. Material examined THAILAND • 39 sh , 22 sp ; Loei Province , Mueang District , Phu Pha Lom Limestone Hill ; 17°33′16.6″ N , 101°52′05.4″ E ; CUMZ 7928 • 6 sh , 12 sp ; same collection data as for preceding; CUMZ 7929 • 48 sh ; Loei Province , Na Duang District , Limestone outcrops at Wat Tham Pha Ya ; 17°34′40.1″ N , 101°53′35.1″ E ; CUMZ 7930 . Description SHELL ( Fig. 4A–B ). Shell strongly depressed to depressed, medium-sized (shell width 17.2–20.1 mm , shell height 8.6–10.0 mm), rather thin to slightly solid and translucent, milky to pale whitish-horny colour, well-rounded body whorl, little elevated spire, impressed suture, obvious varix, and open umbilicus. EXTERNAL FEATURES ( Figs 2A , 5A ). Animal with five well-developed mantle lobes. Left and right shell lobes thin, pale yellowish to fleshy-grey colour and spread with small whitish dots. Three dorsal lobes crescent-shaped and smaller than shell lobes. GENITALIA ( Fig. 5B–D ). Atrium (at) enlarged and very short. Penis (p) rather long cylindrical, penial sheath (ps) very thick and covering entire penis, and penial caecum (pc) rather small protruding. Inner wall of penis covered with trapezoid-shaped penial pilasters (pp) arranged in oblique rows. Epiphallus (e1 + e2) as long as penis: e1 long and slender, and e2 bulbous and about half e1 length. Inner sculpture of e1 with very small and thin longitudinal folds to nearly smooth surface. Inner sculpture of e2 trapezoid to conical pilasters. Epiphallic caecum (ec) long with thick penial retractor muscle (prm) attached at tip. Flagellum (fl) small and short. RADULA ( Fig. 10A ). Teeth arranged in anteriorly V-shaped rows with half row consisting of about 70– 76 teeth at middle plate. Central, lateral, and marginal teeth monocuspid and spatulate-shaped with curved cusp. Fig. 4. Shells of Aenigmatoconcha spp. A –B . A. clivicola Tumpeesuwan & Tumpeesuwan, 2017 , specimen CUMZ 7928 from the type locality (A) and specimen CUMZ 7930 from Loei Province (B). C–F . A. mitis ( Pfeiffer, 1863 ) comb. nov. , syntypes NHMUK ex. Cuming collection (C), specimen CUMZ 7921 from Phetchaburi Province (D), specimen CUMZ 7687 from Kanchanaburi Province (E), and specimen CUMZ 7885 from Nakhon Sawan Province (F). Distribution This species is currently known only from 2 localities: the type locality (Phu Pha Lom) and limestone hills in Loei Province ( Fig. 1 ). Remarks The genitalia were originally described but without examination of the internal sculpture of penis. In this study, we examined 20 adult topotypic specimens to provide descriptions of the penial sheath, penial caecum, and flagellum that were not included in the original description. The penial sheath is very large and covers the entire penis ( Fig. 5B ). The short penial caecum, an extension of the penis, is located near the penis and epiphallus junction ( Fig. 5B ). This character is visible when penial sheath is removed. Its internal sculpture is rather smooth, unlike the penial sculpture, with its trapezoid-shaped pilasters ( Fig. 5C ). The Australian helicarionids, Nitor whitneyae Stanisic, 2010 has a penial caecum while other Nitor taxa do not have a penial caecum (Hyman & Köhler 2018). In Southeast Asian ariophantids, the presence or absence of a penial caecum is a discriminating character among species in genera such as Macrochlamys Gray, 1847 and Taphrenalla Pholyotha & Panha, 2020 , and is supported by molecular studies ( Pholyotha et al. 2018 , 2021 ). The flagellum of A. clivicola is an extension of the epiphallus and is located near the insertion point of the vas deferens. It is somewhat small and short, and bound to the vas deferens by thin connective tissue. This feature is important for spermatophore formation before copulation ( Tompa 1984 ; Baur 2010 ). However, during this study no spermatophores were observed in A. clivicola .