Georissa similis Smith, 1893

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: 63-66

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Georissa similis Smith, 1893


Georissa similis Smith, 1893  Figures 1F, 16 A–K

Georissa similis  Smith, 1893: 351, Plate XXV fig. 26; Thompson and Dance 1983: 126, figs 37, 42, 73-75.

Georissa  sp. 3 (Smith, 1893): Clements et al. 2008: Appendix D.

Type locality.

Gomanton Hill, N. Borneo.

Type material.

Lectotype (Designation by Thompson and Dance 1983). Gomanton Hill, N. Borneo: NHMUK 1892.7.23.51 (glued on paper) (Fig. 1F). Paralectotype. Gomanton Hill, N. Borneo: NHMUK 1892.7.23.52 (1) (glued on paper).

Other material.

Gomanton, N. Borneo: NHMUK (glued on paper), NHMUK (glued on paper). Gomantong hill, Kinabatangan valley, Sandakan, Sabah (05°32.00'N, 118°06.00'E): JJV 1614. Gua Gomantong, Sabah (05°31.03'N, 118°04.01'E): BOR/MOL 52, BOR/MOL 3644. Bukit Mawas, lower Kinabatangan valley, Sabah (05°27.20'N, 118°08.67'E): BOR/MOL 1989. Batu Pangi, Kinabatangan valley, Sandakan, Sabah (05°31.59'N, 118°18.43'E): JJV 9831. Batu Tai (not Bod Tai) near Gomantong, Kinabatangan valley, Sandakan, Sabah (05°32.35'N, 118°10.32'E): JJV 9830, BOR/MOL 2686. Batu Keruak, lower Kinabatangan valley, Sabah (05°31.00'N, 118°17.00'E): BOR/MOL 1466. Ulu Sungai Resang, lower Kinabatangan, Sabah (05°31.00'N, 118°21.00'E): BOR/MOL 1447. Batu Batangan, Sabah (05°27.54'N, 118°06.18'E): MZU/MOL 16.14 (Fig. 16). Gua Madai, Tawau, Sabah (04°44.00'N, 118°08.00'E): BOR/MOL 53, JJV 1738, JJV 7693. Segarong Hills, Bukit Pababola, Semporna, Tawau, Sabah (04°33.00'N, 118°25.00'E): JJV 1772, JJV 1817. Batu Baturong, Tawau, Sabah (04°41.00'N, 118°01.00'E): JJV 1829, BOR/MOL 1446. Limestone hill on N bank Segama river, Tawau, Sabah (05°06.10'N, 118°13.12'E): JJV 7823. Tabin Wildlife reserve, Lahad Datu, Sabah (05°18.81'N, 118°44.65'E): BOR/MOL 54.


Protoconch. Colour: red. Sculpture: rounded to ellipsoidal mesh pattern. Mesh width: 2.8-7.0 µm. Teleoconch. Colour: red. First whorl: convex to flat at the upper part of the whorl. Subsequent whorls: convex. Suture: clearly impressed. Shoulder: narrow to slightly extended. Number of whorls: 2 ½– 3 ¼. SH: 0.96-1.44 mm. SW: 0.85-1.06 mm. SI: 1.13-1.36. Shell sculpture. Radial sculpture: present, dense and regularly spaced, always stronger than the spiral sculpture. Spiral sculpture: present, raised but thin, appearing immediately after the protoconch, spiral sculpture often interrupted due to highly developed radial ribs; the overlapping radial and spiral sculptures form knitted structures on the shell. Aperture. Shape: semi-elliptic to rounded, straight to slightly concave parietal side, palatal edge contiguous with the parietal side, basal side convex. AH: 0.49- 0.64 mm. AW: 0.50-0.67 mm. AI: 0.85-0.98.


Georissa similis  is characterised by the dense radial sculpture. The radial ribs intersect with the thin spiral ribs and form knitted structures throughout the shell surface. The sculpture pattern is similar to G. everetti  but not oblique, and the radial sculpture is more raised in G. similis  . The shell shape is similar to G. corrugata  and G. xesta  , but these species differ entirely in their shell and protoconch sculpture ( G. corrugata  has irregular radial shell sculpture and straight-line protoconch sculpture; G. xesta  does not have radial sculpture and the protoconch sculpture is a mix of irregular shapes).


Georissa similis  is widely distributed in the east of Sabah, from Sandakan in the north to Tawau in the south and Lahad Datu in the east.

Molecular analysis.

ML and Bayesian analyses of G. similis  (16S: n = 5; CO1: n = 5) show that G. similis  form one clade with 100% BS and 100% PP, sister to the group of G. xesta  + G. nephrostoma  + G. bangueyensis  + G. flavescens  .


Uribe et al. (2016) have published the mitochondrial genome of G. similis  (GenBank acc. no. KU342664) which was previously identified as G. bangueyensis  (see phylogenetic trees, Fig. 2A and B). Phylogenetic analyses have shown that it is possible to identify the identity of a Georissa  even when shell data are not available.