Georissa nephrostoma Vermeulen, Liew & Schilthuizen, 2015

Zacaery Khalik, Mohd, P. Hendriks, Kasper, J. Vermeulen, Jaap & Menno Schilthuizen,, 2019, Conchological and molecular analysis of the " non-scaly " Bornean Georissa with descriptions of three new species (Gastropoda, Neritimorpha, Hydrocenidae), ZooKeys 840, pp. 35-86 : 67-70

Georissa nephrostoma Vermeulen, Liew & Schilthuizen, 2015 Figure 18 A–K

Georissa nephrostoma Vermeulen et al., 2015: 34, fig. 20.

Type locality.

Malaysia, Sabah, Sandakan Province, Kinabatangan valley, Batu Keruak 2 near Sukau.

Type material.

Holotype (Holotype by original designation). Malaysia, Sabah, Sandakan Province, Kinabatangan valley, Batu Keruak 2 near Sukau (05°32.00'N, 118°18.00'E): RMNH/MOL 5003955 (not seen, we were unable to locate the material in RMNH collection). Paratypes. Malaysia, Sabah, Sandakan Province. Kinabatangan valley, Batu Keruak 2 near Sukau (05°32.00'N, 118°18.00'E): NHMUK 20150573, BOR/ MOL 1449, BOR/MOL 1450, BOR/MOL 1845, JJV 9795; Batu Pangi (05°31.59'N, 118°18.43'E): BOR/MOL 1452, JJV 9833; Batu Tai near Gomantong (05°32.35'N, 118°10.32'E): JJV 9832; Tandu Batu (05°35.47'N, 118°20.34'E): JJV 9834; Limestone hills near Sukau Police Station: BOR/MOL 2186, BOR/MOL 2153, BOR/MOL 1451.

Other material.

Batu Keruak, Sandakan Province, Sabah (05°32.00'N, 118°18.00'E): BOR/MOL 1454, MZU/MOL 17.29 (Fig. 18). Tandu Batu, Sandakan Province, Sabah (05°35.47'N, 118°20.34'E): BOR/MOL 2685.

Description.

Protoconch. Colour: red to brown. Sculpture: rounded, ellipsoidal to irregular sculptural shape. Mesh width: 2-10 µm. Teleoconch. Colour: red to brown. First whorl: rounded to convex. Subsequent whorls: rounded to convex. Suture: clearly impressed. Shoulder: narrow. Number of whorls: 2 ½– 2 ¾. SH: 0.87-1.24 mm. SW: 0.69-0.92 mm. SI: 1.26-1.43. Shell sculpture. Radial sculpture: absent, densely spaced weak to strong growth lines, no formation of true radial ribs. Spiral sculpture: present, appearing immediately after the protoconch; the ribs are low but narrow to broadly sculpted, regularly spaced, wavy, ca. 12-14 spiral ribs at the upper part of the body whorl; near the aperture, the spiral sculpture is weakened and flattened approaching the columellar region. Aperture. Shape: semi-elliptic, highly convex, and bulky parietal side, palatal side rounded, palatal edge contiguous with the parietal side, basal side convex. AH: 0.40-0.55 mm. AW: 0.43-0.60 mm. AI: 0.92-0.95.

Diagnosis.

Georissa nephrostoma is characterised by the wavy formation of the spiral sculpture and the inflated parietal side of the aperture. The wavy sculpture pattern of G. nephrostoma is similar to G. flavescens but the two species differ entirely based on the shell habitus, where G. flavescens has a more compressed shell habitus. In shell shape, G. nephrostoma resembles G. similis , G. xesta and G. bangueyensis , but none of these species have the uniquely inflated parietal side of the aperture.

Distribution.

Georissa nephrostoma is distributed from Sukau to Gomantong, Kinabatangan region, Sabah.

Molecular analysis.

ML and Bayesian analyses of G. nephrostoma (16S: n = 5; CO1: n = 1) showed that all G. nephrostoma specimens form one clade with 99% BS and 100% PP. The sister group is the G. xesta population from Materis and Ulu Resang ( G. xesta is paraphyletic).