A molecular and conchological dissection of the " scaly " Georissa of Malaysian Borneo (Gastropoda, Neritimorpha, Hydrocenidae) Khalik, Mohd Zacaery Hendriks, Kasper Vermeulen, Jaap J. Schilthuizen, Menno ZooKeys 2018 773 1 55 3FRYJ http://zoobank.org/E88C99A8-8A0D-4438-9699-9AA86CAEE217 Gastropoda Hydrocenidae Georissa CoL Animalia Georissa silaburensis Cycloneritida 0 1 Mollusca species silaburensis  Type locality. Gunong Silabur, Serian, Sarawak, Malaysia ( 00°57.28'N, 110°30.22'E).  Type material. Holotype. Gunong Silabur, Serian, Sarawak, Malaysia ( 00°57.28'N, 110°30.22'E): MZU/MOL 17.88 (leg. MZ Khalik and SK Reduan). Paratypes. Gunong Silabur, Serian, Sarawak, Malaysia ( 00°57.28'N, 110°30.22'E): MZU/MOL 17.01, MZU/MOL 17.02, MZU/MOL 17.03, MZU/MOL 17.04, MZU/MOL 17.05, MZU/MOL 17.06, MZU/MOL 17.07, MZU/MOL 17.08. Borneo, Sarawak, First Division, western side of Gunong Selabor, Semabang entrance to Lobang Batu Cave ( 00°55'N, 110°25'E): NHMUK 1984005 (seen). Each lot of examined paratypes from MZU are more than 50 individuals.  Etymology. Named after Gunung Silabur, Serian, Sarawak, Malaysia, the type locality.  Description. Protoconch. Color: red. Sculpture pattern: meshed - round to irregular mesh pattern. Mesh width: 8-18 µm. Teleoconch. Color: red. First whorl: rounded. Subsequent whorls: convex, number of whorls: 2-2 1/4. SH: 1.59-1.99 mm, SW: 1.50-1.76 mm, SI: 1.06-1.13. Shell sculpture. Radial sculpture: absent or weak to strong growth lines. Spiral sculpture: present, thin but strongly sculpted, continuous ribs, more prominent at the periphery. Scales: two to six or more randomly sculpted series of low and broad horizontal scales, or else acute horizontal nodules on the spiral sculpture, scale series irregularly spaced, which series is the most prominent is not consistent across individuals. Aperture. Shape: rounded. Basal side: rounded, angular at the columellar region. Parietal side: straight, palatal edge attached to slightly removed from the body whorl. AH: 0.95-1.09 mm, AW: 1.00-1.17 mm, AI: 0.92-0.99. Holotype dimension. SH: 1.68 mm, SW: 1.53 mm, AH: 0.95 mm, AW: 1.09 mm.  Figure 13. Georissa silaburensissp. n. A-CHolotype: MZU/MOL 17.88 D-KParatypes: MZU/MOL 17.04. A, D Shell apertural view B Shell side view C Shell rear view E-FShell cross-section from 3D model G-HOperculum frontal and ventral view I Shell top view J Protoconch side view K Close up of protoconch from top at 1000 xmagnification. Scale bars: 500 µm( A-I); 200 µm(J); 10 µm(K).  Cross diagnosis. The shell shape of G. silaburensisis distinct compared to other "scaly group" Georissa. It has rapid shell expansion like G. hoseiand G. scalinella, but G. silaburensishas a different sculpture, consisting of horizontal, rather than vertical or diagonal scales. In addition, the whorls are rounded and convex, with the aperture almost circular, close to G. saulae.  Distribution. Known from the inside of the cave system of Gunung Silabur, Serian, Sarawak.  Molecular analysis. ML and Bayesian analyses show that the individuals of G. silaburensis(16S: n = 10; CO1: n = 9) form one clade with 95% BS and 98% PP, the sister group of G. bauensis.  Discussion.  Georissa silaburensiswas only found inside the cave entrance, with water flowing from the cave roof, and approximately less than 50% light penetration. In shell shape and reduced sculpture, it resembles another cave specialist, G. filiasaulae.