Angustopila megastoma Pall-Gergely & Vermeulen, 2023

Pall-Gergely, Barna, Hunyadi, Andras, Vermeulen, Jaap J., Grego, Jozef, Sutcharit, Chirasak, Reischuetz, Alexander, Dumrongrojwattana, Pongrat, Botta-Dukat, Zoltan, Oerstan, Aydin, Fekete, Judit & Jochum, Adrienne, 2023, Five times over: 42 new Angustopila species highlight Southeast Asia's rich biodiversity (Gastropoda, Stylommatophora, Hypselostomatidae), ZooKeys 1147, pp. 1-177 : 1

Angustopila megastoma Pall-Gergely & Vermeulen sp. nov.

Figs 49 , 50

Type material.

Holotype: Vietnam • 1 empty shell (H: 0.8 mm, D: 1.0 mm); Haiphong Province, Cat Ba Island, near National Park Headquarters, Trung Trang Cave (locality code: Vietnam 02); 20°47.47'N, 106°59.41'E; 5 Sep. 1998; W.J.M. Maassen leg.; RMNH 347770.

Paratypes: Vietnam • 21 adult shells; same data as for holotype; RMNH 347771 • 1 shell; Quang Ninh Province, Halong Bay area, Phao Trong Island (locality code: WMVT.0333); approx. GPS coordinates: 20°49.80'N, 107°08.32'E; 11 Nov. 2003; W.J.M. Maassen leg.; RMNH 347772 • 7 shells; Haiphong Province, Cat Ba Island, Cave Qua Vang, around cave entrance, rocky limestone slope with low, rather mature forest; 20°48.64'N, 107°04.64'E; 100 m a.s.l.; 6 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 16597 • 221 shells; Haiphong Province, Cat Ba Island, Cave Xa Bac, around cave entrance; 20°50.07'N, 106°58.61'E; 30 m a.s.l.; 9 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 16625 • 615 shells; Haiphong Province, Cat Ba Island, Cave Xa Bac, inside cave; 20°50.07'N, 106°58.61'E; 30 m a.s.l.; 9 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 16624 • 10 shells; same data as for preceding; coll. HA • 210 shells; Quang Ninh Province, Halong Bay area, Dao Bo Hon, Song Sot Cave, drift material washed together over sinkhole in cave; 20°50.83'N, 107°05.67'E; 2 Oct. 1998; J.J. Vermeulen & A.J. Whitten leg.; JJV 6237 • 3 shells; Haiphong Province, Cat Ba Island, Cave Qua Vang, inside cave, large, ecologically intact active cave with speleothems; 20°48.64'N, 107°04.64'E; 60 m a.s.l.; 6 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 16596 • 7 shells; Quang Ninh Province, Halong Bay area, unnamed island in Dau Moi Temple area (locality code: WMVT.0338); 20°55.69'N, 107°09.40'E; 13 Sep. 2003; W.J.M. Maassen leg.; RMNH 347773 • 5 shells; Haiphong Province, Cat Ba Island, along trail from headquarters to Viet Hai, along Ao Eck, sampling starting at coordinates, until 0.5 km beyond Ao Eck; 20°48.07'N, 107°00.83'E; 100 m a.s.l.; 4 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 17656 (ex JJV 16618) • 12 shells; Haiphong Province, Cat Ba Island, limestone cliff at SE end of Viet Hai polje, foot of cliff, surrounded by degraded woodland; 20°47.50'N, 107°02.90'E; 30 m a.s.l.; 10 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 16626 • 27 shells; Haiphong Province, Halong Bay area, unnamed island off E Coast Cat Ba, south facing bay with beach and densely vegetated limestone scree slope; 20°45.19'N, 107°4.45'E (approximate GPS data); 1 Oct. 1998; J.J. Vermeulen & K. Anker leg.; JJV 17653 (ex JJV 6236).

Additional material.

Vietnam • 7 j/b shells; same data as for holotype; RMNH 347774 • 4 j/b shells ; Quang Ninh Province, Halong Bay area, Phao Trong Island (locality code: WMVT.0333); approx. GPS data: 20°49.80'N, 107°08.32'E; 11 Nov. 2003; W.J.M. Maassen leg.; RMNH 347775 • 55 j/b shells ; Haiphong Province, Cat Ba Island, Cave Xa Bac , around cave entrance; 20°50.07'N, 106°58.61'E; 30 m a.s.l.; 9 Jun. 2017; J.J. Vermeulen & K. Anker leg.; JJV 17660 (ex JJV 16625 ) .

Diagnosis.

A large, asymmetrically coiled, concave-conical, depressed species with few whorls, weak sculpture, narrow umbilicus, a comparatively large, strongly oblique aperture, and a tiny, pointed parietal tooth (can be absent).

Description.

Shell large for the genus, wider than high, concave-conical, depressed; protoconch consists of 1.25-1.5 whorls, with weak spiral striation preceding the first teleoconch whorl; teleoconch sculpture overall weak, with irregular radial growth lines and dense, weak, rather regular spiral striation (ca. 18-20 spiral striae on body whorl in apertural view); whorls 3.5-3.75, body whorl rounded or depressed-rounded; aperture strongly oblique to shell axis in lateral view; aperture reniform due to concave parietal side (body whorl strongly attached to the penultimate whorl); peristome slightly expanded, not reflected; parietal callus smeared onto penultimate whorl, although its edge is sharp, not fused to penultimate whorl; umbilicus narrow, 1/4 to 1/5 of shell width, its edge slightly covered by reflected peristome edge; aperture sometimes toothless or with low, pointed parietal tooth.

Measurements (in mm).

H = 0.79-0.91, D = 0.91-1.05, H/D*100 = 79.0-91.6 (n = 13), RUD = 24.5-25.5 (n = 3).

Differential diagnosis.

Based on the low conical shell and the narrow umbilicus, this species can be easily recognised and distinguished from other Angustopila species, except for A. thersites sp. nov., which also occurs sympatrically. For comparisons, see under that species.

Tonkinospira defixa is larger, has a more depressed shell, a wider umbilicus, and keeled body whorl, and a stronger spiral sculpture. Tonkinospira chytrophora is larger, has a more globular shell and a stronger sculpture.

Etymology.

The specific epithet Angustopila megastoma (from Greek μέγας = big and στόμα = mouth) refers to the large aperture characteristic for this species.

Distribution.

This species is known from several sites in the Halong Bay Area, northern Vietnam (Fig. 22 ).

Figures

Figure 22. Distribution of Angustopila species.

Figure 49. Angustopila megastoma Pall-Gergely & Vermeulen, sp. nov., (holotype, RMNH 347770). Lateral (A), apical (B), apertural (C) and ventral (D) sides of the shell; sculpture on the protoconch (E), ventral (F) and frontal (G) surface of the body whorl.

Figure 50. Angustopila megastoma Pall-Gergely & Vermeulen, sp. nov., JJV 16596. Lateral (A), apical (B), apertural (C) and ventral (D) sides of the shell; sculpture on the protoconch (E), ventral (F) and frontal (G) surface of the body whorl.