Georissa flavescens Smith, 1895

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 : 72-73

Georissa flavescens Smith, 1895 Figures 1I, 20 A–K

Georissa flavescens Smith, 1895: 126, Plate IV fig. 17; Thompson and Dance 1983: 121.

Type locality.

Gomanton, N.E. Borneo.

Type material.

Lectotype (Designation by Thompson and Dance 1983). Gomanton, NE Borneo: NHMUK 1893.6.8.11 (Fig. 1I). Paralectotypes. Gomanton, NE Borneo: NHMUK 1893.6.8.12-13.

Other material.

Tomanggong Besar 1, Kinabatangan, Sabah: BOR/MOL 7299. Tomanggong Besar 2, Kinabatangan, Sabah: BOR/MOL 7626. Batu Pangi, Kinabatangan valley, Sandakan province, Sabah (05°31.59'N, 118°18.43'E): JJV 9827, BOR/MOL 7288 (Fig. 20), BOR/MOL 9261, BOR/MOL 9325 ( G. flavescens mixed with G. xesta ), BOR/MOL 10816, BOR/MOL 10830, BOR/MOL 10835. Batu Keruak, Kinabatangan, Sabah (05°31.38'N, 118°17.16'E): BOR/MOL 11621.

Description.

Protoconch. Colour: orange. Sculpture: rounded, ellipsoidal to irregular sculptural shape. Mesh width: 2-10 µm. Teleoconch. Colour: orange. First whorl: convex. Subsequent whorls: convex, and slightly angular at the penultimate whorl. Suture: clearly impressed. Shoulder: narrow to slightly extended. Number of whorls: 2 ½– 2 ¾. SH: 0.87-1.20 mm. SW: 0.73-0.95 mm. SI: 1.15-1.26. Shell sculpture. Radial sculpture: absent, weak growth lines. Spiral sculpture: present, appearing immediately after the protoconch, wavy, thin, and regularly arranged ribs at the first whorl, more raised at the later whorls. Aperture. Shape: semi-elliptic, straight to concave parietal side, palatal side rounded, palatal edge contiguous with the palatal side, basal side convex. AH: 0.43- 0.55 mm. AW: 0.47-0.58 mm. AI: 0.82-0.95.

Diagnosis.

Georissa flavescens is characterised by the wavy spiral sculpture, which it only shares with G. nephrostoma , but the latter species, with its narrow spire and inflated columella, is entirely distinct in shell habitus. The shell shape of G. flavescens is similar to G. gomantonensis , G. williamsi , and G. everetti , but its size is reduced compared to these three species.

Distribution.

Georissa flavescens is restricted to four limestone hills, Batu Pangi, Batu Keruak, Batu Gomantong, and Batu Tomanggong, in the Lower Kinabatangan valley of Sabah.

Molecular analysis.

ML and Bayesian analyses of G. flavescens (16S: n = 7; CO1: n = 8) show that G. flavescens forms a monophyletic clade with 100% BS and 100% PP, a sister species of G. bangueyensis .

Discussion.

Thompson and Dance (1983) synonymised G. flavescens to G. gomantonensis , without stating any reason. We find otherwise, that G. flavescens is a valid species based on detailed conchology and molecular analysis.