Georissa pachysoma Vermeulen & Junau, 2007

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 : 62

Georissa pachysoma Vermeulen & Junau, 2007 Figure 15 A–K

Georissa pachysoma Vermeulen & Junau, 2007: 216, fig. 7.

Type locality.

Malaysia, Sarawak, 2nd div.: Lower Tatau River valley, Bukit Sarang group, Bukit Lebik.

Type material.

Holotype (Holotype by original designation). Malaysia, Sarawak, 2nd div.: Lower Tatau River valley, Bukit Sarang group, Bukit Lebik: RMNH/MOL 109084. Paratypes. Malaysia, Sarawak, 2nd div.: Lower Tatau River valley, Bukit Sarang group, Bukit Lebik: JJV 12628 (10), JJV 12837 (2).

Other material.

Bukit Sarang group, Lower Tatau River valley: JJV 12626, JJV 12844, JJV 12845, JJV 12846. Upper Tatau River valley, upper Kakus River limestone scarps: JJV 12847. Bt. Besungai 0.5 m SW of Batu Gading, Long Lama, Baram valley (03°52.00'N, 114°25.00'E): JJV 4940. Slopes and cliffs along path to Great Cave, Niah National Park: JJV 10216. N side of limestone area, Painted Cave, Niah National Park: JJV 10391. Bukit Lebik and Bukit Anyi, Bukit Sarang, Bintulu, Sarawak (02°39.31'N, 113°02.47'E): MZU/MOL 17.62- MZU/MOL 17.84.

Description.

Protoconch. Colour: red to brown. Sculpture: a mix of triangular, rounded, and irregular sculptural shapes. Mesh width: 2-12 µm. Teleoconch. Colour: red to brown. First whorl: convex. Subsequent whorls: convex, broad at the final whorl. Suture: clearly impressed. Shoulder: narrow. Number of whorls: 2 ¾– 3 ¼. SH: 1.20-1.65 mm. SW: 0.95-1.23 mm. SI: 1.19-1.34. Shell sculpture. Radial sculpture: absent, weak growth lines at irregular intervals only. Spiral sculpture: present, rather thin, widely spaced in the centre of the whorls, densely spaced close to the suture and the periphery, ribs appear immediately after the protoconch, ca. 12-15 medium raised spiral ribs, distorted/discontinuous where they are crossed by the growth lines. Aperture. Shape: rounded to semi-elliptic, straight to concave parietal side, palatal side convex and tilted below, palatal edge contiguous with the body whorl, basal side convex. AH: 0.54- 0.70 mm. AW: 0.57-0.72 mm. AI: 0.90-1.00.

Diagnosis.

Georissa pachysoma is characterised by a dark red to brown colour of the shell, similar to G. nephrostoma , but the latter species has wavy spiral ribs while G. pachysoma does not. In shell habitus, G. pachysoma closely resembles G. hungerfordi , but the colour and spiral sculpture of G. hungerfordi (orange in colour in living or freshly dead specimens, with highly raised spiral sculpture) is entirely different from G. pachysoma .

Distribution.

Georissa pachysoma is widely distributed from Bukit Sarang, Bintulu to further north in Baram and Niah, Sarawak.

Molecular analysis.

ML and Bayesian analyses of G. pachysoma (16S: n = 4; CO1: n = 4) show that G. pachysoma forms one clade with 100% BS and 100% PP, sister to the rest of the “non-scaly” group species, except for G. hungerfordi + G. gomantonensis + G. filiasaulae + G. insulae .