Georissa williamsi Godwin-Austen, 1889

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 : 48-51

Georissa williamsi Godwin-Austen, 1889 Figures 1C, 8 A–I

Georissa williamsi Godwin-Austen, 1889: 353, Plate XXXIX fig. 10; Thompson and Dance 1983: 124 (non G. hungerfordi Godwin-Austen, 1889; G. javana Möllendorff, 1897; G. javana intermedia Möllendorff, 1897).

Hydrocena williamsi (Godwin-Austen, 1889): Saul 1967: 109.

Georissa sp.1 (Godwin-Austen, 1889): Clements et al. 2008: Appendix D.

Type locality.

Borneo.

Type material.

Holotype (Holotype by original monotypy). Borneo: NHMUK 1889.12.7.71 (glued on paper) (Fig. 1C) ( Thompson and Dance 1983).

Other material.

Batu Punggul, Sepulut valley, Interior province, Sabah (04°39.00'N, 116°37.00'E): RMNH/MOL 187642, BOR/MOL 57, JJV 1907. Gua Pungiton, Sepulut valley, Interior province, Sabah (04°42.41'N, 116°36.04'E): BOR/MOL 55, JJV 7543. Bukit Tinahas, Sepulut valley, East end of Batu Punggul limestone, Interior province, Sabah (04°38.28'N, 116°37.05'E): JJV 7623. Tinahas limestone hill, Interior Province, Sabah (04°38.46'N, 116°37.08'E): RMNH/MOL 333928, RMNH/MOL 334016, BOR/MOL 56, BOR/MOL 59. Batu Temurung, Sepulut valley, Interior province, Sabah (04°42.45'N, 116°34.40'E): BOR/MOL 58, BOR/MOL 60, JJV 8037. Simbaluyon limestone hill, Interior Province, Sabah, (04°43.25'N, 116°34.22'E): RMNH/MOL 333922, RMNH/MOL 333946 (Fig. 8), RMNH/MOL 334007. Batu Baturong ca. 50 km W.S.W. of Lahad Datu, Tawau province, Sabah (04°41.00'N, 118°1.00'E): JJV 1830. Madai limestone hill, Tawau Province, Sabah (04°43.66'N, 118°10.71'E): RMNH/MOL 337817, RMNH/MOL 337827, RMNH/MOL 337834. Cave on Teck Guan estate, Lahad Datu, Sabah: ZMA/MOLL 315607, ZMA/MOLL 315608, ZMA/MOLL 315609, ZMA/MOLL 315622.

Description.

Protoconch. Colour: orange to red. Sculpture: a mix of rounded, ellipsoidal to irregular sculptural shape. Mesh width: 2-6 µm. Teleoconch. Colour: orange to red. First whorl: convex. Subsequent whorls: convex. Suture: clearly impressed. Shoulder: narrow. Number of whorls: 3-3 ¼. SH: 1.58-1.91 mm. SW: 1.17-1.42 mm. SI: 1.30-1.38. Shell sculpture. Radial sculpture: absent, only weak to strong growth lines are visible at irregular intervals. Spiral sculpture: present, thin, regularly spaced at the first whorl, appearing immediately after the protoconch, on later whorls the spiral sculpture weakens and becomes distorted by the growth lines; more than 20 spiral ribs on the body whorl of the adult individual. Aperture. Shape: semi-elliptic, straight to concave parietal side, palatal side rounded, palatal edge contiguous with the body whorl, basal side slightly convex. AH: 0.63- 0.81 mm. AW: 0.71-0.87 mm. AI: 0.89-0.95.

Diagnosis.

Georissa williamsi has a broad final whorl, in which it is similar to G. gomantonensis and G. everetti . However, these three species are all distinctly sculptured, where G. gomantonensis has raised spiral sculpture, G. everetti has oblique spiral sculp ture, but G. williamsi has thin, hardly raised, and densely arranged spiral sculpture (4-6 ribs in every 0.1 mm), despite the similar shell habitus.

Distribution.

Georissa williamsi occurs over a large part of Sabah from the Sepulut valley in the west-central to Tawau and Lahad Datu in the east.

Discussion.

The type locality of G. williamsi is ‘Borneo’, with no specific location stated by Godwin-Austen (1889). Saul (1966) in her note on "Shell collecting in the limestone cave of Borneo" mentioned that during her trip to Lahad Datu, Sabah, they collected G. williamsi (syn. Hydrocena williamsi ). Based on the characters of G. williamsi described by Godwin-Austen (1889) and the type material we have examined, the species does not have very prominent spiral sculpture. Georissa williamsi was previously misinterpreted as having highly raised spiral sculpture, and the name was therefore misapplied to forms like G. hungerfordi , G. insulae , and G. javana ( Thompson and Dance 1983; Phung et al. 2017; Vermeulen and Whitten 1998).