Aenigmatoconcha sumonthai Tumpeesuwan & Tumpeesuwan, 2018

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 : 70-72

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.

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 ).

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. 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.

Fig. 8. Genital system of Aenigmatoconcha sumonthai Tumpeesuwan & Tumpeesuwan, 2018, specimen CUMZ 7922 from the type locality. A. General view of genitalia; inset showing flagellum encircled with a loose tissue before clearing it out. B. Internal structure of penis; inset showing penial sculpture. C. Internal structure of epiphallus and epiphallic caecum. 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.