Angustopila maasseni 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 maasseni Pall-Gergely & Vermeulen sp. nov.

Fig. 46

Type material.

Holotype: Vietnam • 1 empty shell (H: 0.62 mm, D: 0.7 mm); Quang Ninh Province, Halong Bay area, Phao Trong Island (locality code: WMVT.0333); 20°49.80'N, 107°08.32'E; 11 Sep. 2003; W.J.M. Maassen leg.; RMNH.5006715.

Paratypes: Vietnam • 1 shell; same data as for holotype; NMBE 550643 • 9 shells; same data as for holotype; RMNH 347768 • 1 shell; Quang Ninh Province, Halong Bay area, small (ca. 150 m longest section) sparsely vegetated limestone rock island; 20°52.88'N, 107°07.63'E; 3 Oct. 1998; J.J. Vermeulen & T. Whitten leg.; JJV 6227.

Additional material.

Vietnam • 3 juvenile shells; same data as for holotype; RMNH 347769 .

Diagnosis.

A small, depressed-globular Angustopila species with a reniform aperture having an apertural axis oblique to shell axis, and a strong parietal tooth.

Description.

Shell small for the genus, wider than high; off-white, depressed-globular form with domed spire; body whorl widest from standard apertural view; protoconch consists of 1.25-1.5 whorls, microstructure pitted and granular with a powdery superficial texture, no spiral striation discernible; teleoconch ornamented by some fine radial growth lines and stronger, equidistantly-arranged spiral striae (ca. 13-15 on body whorl from standard apertural view); whorls 3.5, slightly shouldered; aperture slightly oblique to shell axis from lateral view; umbilicus wide; aperture reniform with strong indentation along the outer parietal margin; apertural axis joins shell axis under a large angle; sinulus wide; peristome expanded, not reflected; parietal callus strongly protruding but in line with curvature of penultimate whorl and beyond aperture edge (profile) in lateral view [Fig. 46C ], detached from penultimate whorl; parietal tooth relatively weak, low, quite long, nearly reaching peristome.

Measurements (in mm).

H = 0.6-0.63, D = 0.67-0.97 H/D*100 = 88.4-94 (n = 5), RUD = 28.2-29.7 (n = 2).

Differential diagnosis.

Angustopila somsaki sp. nov. is slightly larger, has a wider umbilicus, has a vestigial palatal tooth, and a protoconch with spiral striation, its reniform aperture is vertically positioned (not pushed from parietal direction causing it to be positioned sideways), and the apertural axis (sinulus-base) is oriented in a smaller angle to the shell axis. In contrast, the aperture of A. maasseni sp. nov. is rather kidney-shaped due to the forward angle of the body whorl, whereby the apertural axis is positioned at a larger angle in respect to the shell axis. Angustopila psammion has a smaller, more depressed shell than A. maasseni sp. nov., and has a narrower umbilicus. Moreover, the parietal tooth of that species is pointed and short, and does not reach the peristome edge. In contrast, the parietal tooth is elongated and reaches the peristome in A. maasseni sp. nov. See also under A. cicatricosa sp. nov.

Etymology.

This new species is named after and dedicated to our friend and malacologist, Wim Maassen (1947-2021), who collected several of the new species described in this study.

Distribution.

This species is known from two nearby localities in the Halong Bay, northern Vietnam (Fig. 24 ).

Figures

Figure 24. Distribution of Angustopila species in the Halong Bay area.

Figure 46. Angustopila maasseni Pall-Gergely & Vermeulen, sp. nov. (holotype, RMNH. 5006715). Apertural (A), ventral (B), lateral (C), and apical (D) sides of the shell; aperture (E, F); sculpture of the protoconch (G), ventral (H) and frontal (I) surface of the body whorl.