Georissa gomantonensis Smith, 1893

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 : 55-58

Georissa gomantonensis Smith, 1893 Figures 1E, 12 A–K

Georissa gomantonensis Smith, 1893: 351, Plate XXV fig. 25; Thompson and Dance 1983: 121, figs 36, 58-60; Schilthuizen et al. 2003: 41.

Georissa gomantongensis Smith: Vermeulen and Junau 2007: 217; Clements et al. 2008: 2762; Khalik et al. 2018: 19, fig. 1J.

Type locality.

Gomanton, N. Borneo.

Type material.

Holotype (Holotype by original monotypy). Gomanton, N. Borneo: NHMUK 1892.7.20.39 (glued on paper) (Fig. 1E) ( Thompson and Dance 1983).

Other material.

Gua Gomantong, Kinabatangan, Sabah (05°32.00'N, 118°06.00'E): BOR/MOL 7632, BOR/MOL 7389 (Fig. 12), JJV 1612. Batu Tai (not Bod Tai) near Gomantong, Kinabatangan valley, Sabah (05°32.35'N, 118°10.32'E): JJV 9590. Batu Pangi, Kinabatangan valley, Sandakan province, Sabah (05°31.59'N, 118°18.43'E): BOR/MOL 10829, JJV 9648. Batu Keruak 2 near Sukau, Kinabatangan valley, Sabah (05°32.00'N, 118°18.00'E): JJV 9801. Kampung, Kinabatangan, Sabah (05°30.90'N, 118°16.86'E): BOR/MOL 10866, BOR/MOL 12545. Batu Tomanggong Besar 1, Kinabatangan, Sabah (05°31.26'N, 118°18.06'E): BOR/MOL 10561, BOR/MOL 11296. Batu Tomanggong Besar, lower Kinabatangan valley, Sandakan, Sabah (05°31.02'N, 118°18.21'E): BOR/MOL 2253, BOR/MOL 2282. Tomanggong 2, lower Kinabatangan valley, Sandakan, Sabah (05°31.00'N, 118°18.00'E): BOR/MOL 1462. Batu Keruak, Kinabatangan, Sabah (05°31.32'N, 118°17.10'E): BOR/MOL 1460, BOR/MOL 1883, BOR/MOL 11697. Bod Tai, Kinabatangan, Sabah (05°31.00'N, 118°13.00'E): BOR/MOL 1465, BOR/MOL 11256. Bukit Mawas, lower Kinabatangan valley, Sabah (05°27.00'N, 118°08.00'E): BOR/MOL 1463, BOR/MOL 1990. Unnamed hill 1, lower Kinabatangan valley, Sabah (05°31.11'N, 118°17.23'E): BOR/MOL 2152, BOR/MOL 2185. Unnamed hill 2, lower Kinabatangan valley, Sabah (05°30.00'N, 118°17.00'E): BOR/MOL 1461. Sabahmas Cave, Segama valley, Tawau, Sabah (05°08.52'N, 118°26.01'E): JJV 7452. Segama River, Segama valley, near bridge of road Sandakan to Lahad Datu, Tawau, Sabah (05°06.10'N, 118°13.12'E): JJV 7496. Tabin River, Segama valley, Sandakan, Sabah (05°18.49'N, 118°44.39'E): JJV 7753. Batu Temurung, Sepulut valley, Sabah (04°42.45'N, 116°34.40'E): JJV 8035. Pulau Mataking, Easternmost island of the Semporna-Sulu Chain, Sandakan: JJV 11523. Tabin Wildlife Reserve, Lahad Datu, Sabah (05°18.81'N, 118°44.65'E): BOR/MOL 19, BOR/MOL 20. Ulu Sungai Resang, lower Kinabatangan limestone hill, Sabah (05°31.00'N, 118°21.00'E): BOR/MOL 1464. N end of limestone ridge on E bank of Tabin River Sandakan Province, Sabah (05°18.04'N, 118°44.03'E): BOR/MOL 18. Batu Temurung, Sepulut Valley, Interior province, Sabah (04°42.04'N, 116°34.04'E): BOR/MOL 17.

Description.

Protoconch. Colour: greenish yellow. Sculpture: ellipsoidal mesh to irregular sculptural shape. Mesh width: 4-16 µm. Teleoconch. Colour: greenish yellow. First whorl: convex. Subsequent whorls: convex. Suture: well-impressed. Shoulder: slightly extended, with a row of regularly spaced granules. Number of whorls: 3-3 ¼. SH: 1.95-2.17 mm. SW: 1.67-1.68 mm. SI: 1.17-1.29. Shell sculpture. Radial sculpture: absent, only weak growth lines present throughout the shell surface. Spiral sculpture: present, strongly sculpted spiral ribs, at regular intervals, appearing immediately after the protoconch, sometimes distorted/discontinuous by growth lines, reduced in strength when reaching the columellar region, ca. 14-18 spiral ribs visible on the body whorl in the adult individual. Aperture. Shape: rounded to slightly ovoid, straight to concave parietal side, palatal edge contiguous with the body whorl, basal side convex. AH: 0.94- 0.97 mm. AW: 1.04-1.08 mm. AI: 0.87-0.92.

Diagnosis.

Georissa gomantonensis is characterised by its bright greenish yellow colour, broad final whorl, and strong spiral sculpture. The spiral sculpture pattern is similar to G. insulae , but the shell habitus of G. gomantonensis is much broader and inflated. Georissa everetti and G. williamsi have a similar shell habitus as G. gomantonensis , but differ because lacking of the oblique ( G. everetti ) and densely arranged ( G. williamsi ) spiral sculpture.

Distribution.

Georissa gomantonensis is widely distributed throughout Sabah. More commonly found in the vegetation of the limestone forest, rather than on the limestone rocks themselves.

Molecular analysis.

ML and Bayesian analyses show that the individuals of G. gomantonensis (16S: n = 2; CO1: n = 2) form a monophyletic group with 100% BS and 100% PP, sister group to the paraphyletic G. saulae + G. filiasaulae .