Aenigmatoconcha mitis ( Pfeiffer, 1863 ) Pholyotha, Arthit, Sutcharit, Chirasak, Tongkerd, Piyoros & Panha, Somsak, 2021

Pholyotha, Arthit, Sutcharit, Chirasak, Tongkerd, Piyoros & Panha, Somsak, 2021, Systematic revision of the limestone karst-restricted land snail genus Aenigmatoconcha (Eupulmonata: Helicarionidae), with description of a new species, European Journal of Taxonomy 767, pp. 55-82 : 66-70

Aenigmatoconcha mitis ( Pfeiffer, 1863) comb. nov.

Figs 1 , 2B , 4C–F , 6 , 10B

Helix mitis Pfeiffer, 1863 [1862]: 268. Type locality: Lao Mountains, Camboja [Lao Mountains, Cambodia].

Helix mitis – Pfeiffer 1868: 141. — Tryon 1886: 171.

Ariophanta (Kaliella) mitis – Fischer 1891: 21.

Hyalinia mitis – Fischer & Dautzenberg 1904: 396.

Macrochlamys (?) mitis – Inkhavilay et al. 2019: 78 , 79, fig. 37b.

Material examined

Syntypes CAMBODIA • 2 sh; “Lao Mountains, Camboja ” [ Lao Mountains , Cambodia]; NHMUK ex. Cuming collection .

Other material

THAILAND • 37 sh, 16 sp; Nakhon Sawan Province, Mueang District, Limestone outcrops at Wat Tham Bo Ya; 15º43′47.3″ N, 99º56′44.7″ E; CUMZ 7708 • 30 sh, 15 sp; same collection data as for preceding; CUMZ 7885 • 8 sh, 21 sp; Nakhon Sawan Province, Krok Phra District, Limestone outcrops at Wat Khao Tham Phra; 15°33′30.2″ N, 99°57′28.1″ E; CUMZ 7849 • 3 sp; Kanchanaburi Province, Sai Yok District, Limestone outcrops at Wat Thep Thepa Satthatham; 14°03′56.6″ N, 99°11′45.7″ E; CUMZ 7913 • 21 sh, 24 sp; Kanchanaburi Province, Mueang District, Limestone outcrops at Wat Tham Charoentham; 13°55′59.1″ N, 99°27′59.9″ E; CUMZ 7687 • 3 sp; Kanchanaburi Province, Tha Muang District, Limestone outcrops at Wat Tham Faet; 13°57′52.5″ N, 99°34′56.1″ E; CUMZ 7914 • 30 sh, 1 sp; Kanchanaburi Province, Dan Makham Tia District, Limestone outcrops at Wat Tham Khao Cha Ang; 13°48′08.4″ N, 99°26′33.2″ E; CUMZ 7247 • 4 sh, 3 sp; Phetchaburi Province, Khao Yoi District, Limestone outcrops at Wat Khiri Wong; 13°20′03.2″ N, 99°45′19.0″ E; CUMZ 7917 • 1 sh, 15 sp; Phetchaburi Province, Khao Yoi District, Limestone outcrops at Wat Puang Malai; 13°18′46.0″ N, 99°47′02.2″ E; CUMZ 7921 • 9 sh; same collection data as for preceding; CUMZ 7938 • 5 sh, 14 sp; Phetchaburi Province, Tha Yang District, Limestone outcrops at Wat Khao Krachiu; 12°57′41.3″ N, 99°54′49.3″ E; CUMZ 7918 • 3 sh, 16 sp; Phetchaburi Province, Cha-am District, Limestone outcrops at Khao Nang Panthurat; 12°50′20.5″ N, 99°57′11.6″ E; CUMZ 7920 • 2 sh, 2 sp; Phetchaburi Province, Cha-am District, Limestone outcrops at Tham Chaeng Bureau of Monks; 12°49′44.3″ N, 99°56′27.1″ E; CUMZ 7919 • 4 sh, 7 sp; Prachuap Khiri Khan Province, Mueang District, Limestone outcrops at Khao Lom Muak; 11°47′03.0″ N, 99°48′56.3″ E; CUMZ 7915 • 3 sh, 8 sp; Prachuap Khiri Khan Province, Mueang District, Limestone outcrops at Khao Ta Mong Lai; 11 o 50′07.3″ N, 99 o 49′50.1″ E; CUMZ 7916 .

Description

SHELL ( Fig. 4C–F ). Shell depressed to globosely depressed, medium-sized (width 12.3–18.1 mm, height 6.9–9.9 mm), rather thin, and translucent. Shell surface smooth and glossy. Shell colour whitish to very pale horny-white. Whorls: 5–5½, regularly increasing in size; varix present; suture rather wide and shallow. Spire rather elevated. Last whorl broad and well-rounded. Aperture obliquely oval-lunate in shape; peristome simple. Columellar margin simple, slightly expanded near umbilicus. Umbilicus open and deep.

EXTERNAL FEATURES ( Fig. 2B ). Living snails with reticulated skin and pale yellowish to dark grey body. Five well-developed mantle lobes; left and right shell lobes thin, pale yellowish, spread with small whitish dots, and left shell lobe larger than right shell lobe. Three dorsal lobes broad and crescentshaped; right dorsal lobe larger than anterior and posterior left dorsal lobes. Caudal fossa present; caudal horn raised, rather large, and whitish to pale fleshy-grey in colour.

GENITALIA ( Fig. 6 ). Atrium (at) enlarged and very short. Penis (p) long, cylindrical, and with slightly thick penial sheath (ps) encircling about half of penis length. Inner sculpture of penis with very small and oblique wrinkled penial pilasters (pp), and one large longitudinal fold running the length of the entire penis chamber. Epiphallus (e1 + e2) approximately as long as penis: e1 slender and narrower than penis, and e2 shorter and bulbous shape. Inner sculpture of e1 with very small thin longitudinal folds to nearly smooth surface with one thickened longitudinal fold, and inner sculpture of e2 with large papillae arranged in oblique rows. Epiphallic caecum (ec) very short; penial retractor muscle (prm) thin and attached at tip. Flagellum (fl) small and rather short. Vas deferens (vd) very long and thin. Vagina (v) very short and enlarged. Gametolytic duct (gd) long, slender, and enlarged near vagina; gametolytic sac (gs) very large and oblong shape. Free oviduct (fo) cylindrical, long, and encircled with thick tissue near vagina.

RADULA ( Fig. 10B ). Teeth arranged in anteriorly V-shaped rows with half row consisting of about 76– 79 teeth at middle plate. Central teeth symmetrical monocuspid, and spatulate-shaped with curved cusp. Lateral and marginal teeth undifferentiated, asymmetrical monocuspid, spatulate-shaped with curved cusp, and outermost teeth gradually reduced in size.

Distribution

The distribution of Aenigmatoconcha mitis is wider than all other recognised species. This species can be found in limestone areas ranging from central (Nakhon Sawan Province) to southern (Prachuap Khiri Khan Province) Thailand ( Fig. 1 ).

Remarks

This species was originally described by L. Pfeiffer (1863) based on specimens in the collection of H. Cuming obtained from Henry Mouhot. The collection locality was brief: “Lao Mountains, Camboja ”. However, Mouhot’s recorded localities were generally imprecise and referred to a wide geographical area, for example “ Siam ”, “Lao Mountains, Camboja ” and “ Camboja ”. This has made it difficult to infer more precise type localities of several land snail species described from Mouhot’s specimens. No additional specimen records or literature references are available for this species until now. The most recent works on land snails from Laos and southern Cambodia confirmed the existence of A. mitis ( Inkhavilay et al. 2019; Sutcharit et al. 2020c). Based on the recorded itinerary, H. Mouhot had travelled to “Pechaburi” [Petchaburi Province] in 1861, and clearly stated that he had visited caves and several hills during his four-month stay ( Mouhot 1864: 57; Ashburton 1864: map). We have surveyed several limestone hills in western and peninsular Thailand and encountered numbers of empty shells and living specimens that well-matched with the type specimens of “ Helix mitis Pfeiffer, 1863 ” ( Fig. 4C ). Therefore, peninsular Thailand (Petchaburi Province; Fig. 1 ) might be the area where H. Mouhot collected this species.

Aenigmatoconcha mitis exhibits a rather wide range of shell shape variation from depressed ( Fig. 4F ) to somewhat globose ( Fig. 4C, D ). However, the genitalia of these shell morphs are identical and the COI phylogeny also supports that all shell morphs are grouped together within the A. mitis clade ( Fig. 2 ).

Figures

Fig. 1. Geographic distribution of four species of Aenigmatoconcha Tumpeesuwan & Tumpeesuwan, 2017 based on specimens examined herein.

Fig. 2. Maximum likelihood tree of Aenigmatoconcha Tumpeesuwan & Tumpeesuwan, 2017 based on the COI gene dataset. Numbers on nodes indicate the ML bootstrap values (left) and Bayesian posterior probabilities (right) values. Pictures of living snails are not to scale.

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).

Fig. 6. Genital system of Aenigmatoconcha mitis (Pfeiffer, 1863) comb. nov., specimen CUMZ 7687 from Kanchanaburi Province. A. General view of genitalia. B. Internal structure of penis, epiphallus, and epiphallic caecum; inset showing penial sculpture. White arrow indicates the junction between the penis and epiphallus.

Fig. 10. Radula morphology of Aenigmatoconcha spp. A. A. clivicola Tumpeesuwan & Tumpeesuwan, 2017, specimen CUMZ 7929 from Loei Province. B. A. mitis (Pfeiffer, 1863) comb. nov., specimen CUMZ 7687 from Kanchanaburi Province. C. A. sumonthai Tumpeesuwan & Tumpeesuwan, 2018, specimen CUMZ 7922 from Chumphon Province. D. A. eunetis Pholyotha & Panha sp. nov., paratype CUMZ 7933 from Uthai Thani Province. Central tooth in yellow. Scale bars: A–C = 100 μm; D = 50 μm.