Georissa silaburensis, Khalik, Mohd Zacaery, Hendriks, Kasper, Vermeulen, Jaap J. & Schilthuizen, Menno, 2018

Khalik, Mohd Zacaery, Hendriks, Kasper, Vermeulen, Jaap J. & Schilthuizen, Menno, 2018, A molecular and conchological dissection of the " scaly " Georissa of Malaysian Borneo (Gastropoda, Neritimorpha, Hydrocenidae), ZooKeys 773, pp. 1-55 : 1

Georissa silaburensis sp. n.

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 ¼. 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.

Cross diagnosis.

The shell shape of G. silaburensis is distinct compared to other "scaly group" Georissa . It has rapid shell expansion like G. hosei and G. scalinella , but G. silaburensis has 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 silaburensis was 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 .