Opisthoporus thuathienhuensis D. S. Do, T. C. Bui & V. N. Do, 2020

Sang, Do Duc, Chinh, Bui Thi & Nhuong, Do Van, 2020, The land snail genus Opisthoporus Benson in L. Pfeiffer, 1851 (Gastropoda: Caenogastropoda: Cyclophoridae) from Vietnam, with description of a new species, Raffles Bulletin of Zoology 68, pp. 103-111 : 108-109

Opisthoporus thuathienhuensis D. S. Do, T. C. Bui & V. N. Do , new species

( Figs. 1 , 2 H–K, 3C, F, I; Table 1, 2)

Material examined. Holotype (1 shell, shell height 10.1 mm, shell width 16.0 mm; Figs. 2H, I , 3C, F, I ) ( VNMN _ IZ 000.000.176), Vietnam, Thua Thien Hue Province , Nam Dong District , Thuong Quang Commune, Limestone mountain, 217 m a.s.l., 16°06′56″N, 107°38′32″E, coll. T.C. Bui, 16 September 2017 ; Paratypes: 6 paratypes ( ZMHU. MOL 001 ) , 2 paratypes ( ZRC.MOL. 15631), same data as holotype .

Etymology. The specific epithet “ thuathienhuensis ” is derived from its type locality Thua Thien Hue Province in central Vietnam, with the Latin suffix “-ensis” added to form an adjective.

Diagnosis. Shell devoid of patterns on both dorsal and ventral sides of shell. Small breathing tube in the form of

an inverted U-shape, distal end touching the last whorl. Peristome single, slightly thickened, not expanded.

Description. Shell slightly thick, medium sized (shell height 8.7–12.3 mm, shell width 14.0–19.5 mm), sub-discoidal with wide umbilicus. Spire low, obtuse. Whorls 3¾–4, well-rounded. The last whorl is partially detached from the penultimate whorl. Sutures deeply impressed. Umbilicus wide, about ⅓ of shell diameter. Periostracum brown, translucent, shiny, without spiral sculpture. Protoconch smooth and glossy, two whorls. Teleoconch sculptured with irregularly spaced, inconspicuous growth lines, spiral sculpture virtually absent. Breathing tube present near the suture, situated a little distance (ca. 1.4–2.2 mm) from the peristome. Breathing tube curved, forming a reversed U-shape, the distal end pointing back towards the last whorl. Aperture circular, with pale yellow, slightly thickened, and non-expanded peristome.

Operculum solid, round, bi-layered, the outer calcified layer thicker than the inner corneous layer. Outer surface slightly concave, covered with fine growth lines, nucleus usually deeply sunken. Inner surface smooth, glossy, and concave.

Distribution. The new species is thus far known only from the limestone mountain in Thuong Quang Commune, Nam Dong District, Thua Thien Hue Province, central Vietnam.

Remarks. The new species differs distinctly from O. beddomei and O. lubricus by its single peristome without an expanded lip and small breathing tube, which forms an inverted U-shape with distal end touching the last whorl.

Figures

Fig. 1. Approximate localities of Opisthoporus spp. in Vietnam. (1): Opisthoporus beddomei; (2): Opisthoporus lubricus; (3): Opisthoporus thuathienhuensis, new species. The numbered locality names are detailed in Table 1.

Fig. 2. Shell (apertural view, dorsal view, ventral view, and side view) and operculum (outer surface, inner surface, and side view) of Opisthoporus spp. in Vietnam. A–D, Opisthoporus beddomei Dautzenberg & Fischer, 1908; A, B, ZMHU/5; C, from Dautzenberg & Fischer, 1908; D, from Kobelt, 1913. E–G, Opisthoporus lubricus Dautzenberg & Fischer, 1908; E, ZMHU/4; F, from Kobelt, 1913; G, from Dautzenberg & Fischer, 1908. H–K, Opisthoporus thuathienhuensis, new species; H, I, holotype VNMN_IZ 000.000.176; J, K, paratypes ZRC.MOL. 15631. Photographs by D.S. Do and T.S. Nguyen.

Fig. 3. Comparison of shell profile, breathing tube, and peristome of Opisthoporus spp. in Vietnam. A, D, G, Opisthoporus beddomei (ZMHU/5), with oblique breathing tube and double peristome; B, E, H, Opisthoporus lubricus (ZMHU/4), with forward pointing breathing tube and double peristome; C, F, I, Opisthoporus thuathienhuensis, new species (holotype VNMN_IZ 000.000.176), with inverted U-shaped breathing tube and single peristome. Photographs by D.S. Do and T.S. Nguyen.