Georissa scalinella (van Benthem-Jutting, 1966)

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 scalinella (van Benthem-Jutting, 1966)

Hydrocena scalinella van Benthem-Jutting, 1966: 39, fig. 1; Saul 1967: 108.

Georissa scalinella (van Benthem-Jutting): Thompson and Dance 1983: 119; Phung et al. 2017: 68, fig. 8B.

Type locality.

Lahad Datu Caves on Teck Guan Estate, Sabah.

Type material.

Holotype. Lahad Datu Caves on Teck Guan Estate, Sabah: ZMA/MOLL 135736 (seen). Paratypes. Lahad Datu Caves on Teck Guan Estate, Sabah: ZMA/MOLL 135735 (seen), ZMA/MOLL 315596 (seen).

Description.

Protoconch. Color: orange to red. Sculpture: smooth to meshed - semi oval mesh to undefined mesh pattern. Mesh width: 7-17 µm. Teleoconch. Color: orange. First whorl: flat at the shoulder. Subsequent whorls: flat above, slightly rounded below the periphery. Total number of whorls: 2 ¼ -2 ½. SH: 1.56-1.80 mm, SW: 1.46-1.65 mm, SI: 1.03-1.15. Shell sculpture. Radial sculpture: absent, only weak to strong growth lines are visible. Spiral sculpture: present, and strongly sculpted, with continuous and discontinuous ribbing. Scales: a series of acute scales, low to highly projected, and regularly spaced. Intercept between growth lines and spiral ribbings form small pointed scale structures throughout the length of the body whorl. Aperture. Shape: oval. Basal side: rounded, angular at the columellar region. Parietal side: straight, palatal edge attached to the body whorl. AH: 0.78-0.94 mm, AW: 0.97-1.12 mm, AI: 0.75-0.89. Holotype dimension. SH: 1.88 mm, SW: 1.72 mm, AH: 0.84 mm, AW: 1.18 mm.

Cross diagnosis.

Georissa scalinella has a series of scales at the shoulder. In habitus and scale characters, it resembles G. pyrrhoderma from Gunung Silabur, Sarawak. The angular shoulder and small scale-like nodular structure at the intersection of strong spiral ribbings and growth lines are diagnostic for G. scalinella .

Distribution.

Known only from the type locality, Teck Guan Estate, Lahad Datu, Sabah, and also reported by Phung et al. (2017) at Pulau Tiga, Sandakan, Sabah. However, this may also refer to one of the other "scaly group" species from Sabah.

Discussion.

Georissa scalinella was first described as Hydrocena scalinella van Benthem-Jutting, 1966, before reclassified as Georissa by Thompson and Dance (1983). van Benthem-Jutting (1966) described G. scalinella as having strong spiral ribbing and multiple lines of scales.