Georissa xesta Thompson & Dance, 1983

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 : 66-67

Georissa xesta Thompson & Dance, 1983 Figures 1G, 17 A–K

Georissa xesta Thompson & Dance, 1983: 125, figs 69-70.

Type locality.

A small limestone ridge quarried for rock 5 mi W Kudat, Sabah, Borneo (06°57.00'N, 116°48.00'E).

Type material.

Holotype (Holotype by original designation). A small limestone ridge quarried for rock 5 mi W Kudat, Sabah, Borneo (06°57.00'N, 116°48.00'E): UF 35968 (not seen). Paratypes. A small limestone ridge quarried for rock 5 mi W Kudat, Sabah, Borneo (06°57.00'N, 116°48.00'E): UF 35969 (not seen), UF35970 (not seen), SMF 255740/6 (not seen), NHMUK 1984.006 (5) (Fig. 1G), JJV 13424.

Other material.

Kinabatangan valley, Batu Tulug (Batu Putih) along road Lahad Datu-Sandakan, N of bridge over Kinabatangan River, Sandakan province, Sabah (05°25.00'N, 117°56.00'E): JJV 1481. Kinabatangan valley, Batu Keruak 2 near Sukau, Sandakan province, Sabah (05°32.00'N, 118°18.00'E): JJV 9786. Kinabatangan valley, Batu Tomanggong Kecil, Sandakan province, Sabah (05°30.12'N, 118°18.10'E): JJV 9828. Batu Tomanggong Besar, Kinabatangan valley, Sandakan, Sabah (05°31.02'N, 118°18.21'E): BOR/MOL 1437, BOR/MOL 2252, BOR/MOL 2281. Batu Tomanggong Besar 2, Kinabatangan valley, Sandakan, Sabah (05°31.16'N, 118°18.33'E): BOR/MOL 1440. Batu Tomanggong Kecil, Kinabatangan valley, Sandakan, Sabah (05°30.21'N, 118°18.18'E): BOR/MOL 2025, BOR/MOL 2053. Batu Keruak, Kinabatangan valley, Sandakan, Sabah (05°32.00'N, 118°18.00'E): BOR/MOL 2687. Lower Kinabatangan valley, Sabah; Unnamed limestone hill 1 (05°31.11'N, 118°17.23'E): BOR/MOL 2151, BOR/MOL 2184, BOR/MOL 2217; Unnamed limestone hill 2 (05°30.00'N, 118°17.00'E): BOR/MOL 1441. Batu Materis, Kinabatangan valley, Sabah (05°31.21'N, 118°01.31'E): BOR/MOL 2113, BOR/MOL 2083. Bod Tai, Kinabatangan valley, Sabah (05°31.00'N, 118°13.00'E): BOR/MOL 1443. Bukit Mawas, lower Kinabatangan valley, Sabah: BOR/MOL 1444. Pangi, Kinabatangan valley, Sandakan province, Sabah (05°31.59'N, 118°18.43'E): BOR/MOL 1442. Ulu Sungai Resang, lower Kinabatangan valley, Sabah (05°31.00'N, 118°21.00'E): BOR/MOL 1438, BOR/MOL 7303 (Fig. 17), BOR/MOL 7311. Segama valley, ‘Kirk’s Cave’ 8 km N of Lahad Datu, Tawau province, Sabah (05°04.00'N, 118°16.00'E): JJV 1236. Segama valley, hill NW of crossing road Sandakan-Lahad Datu with the Segama River, Tawau province, Sabah (05°06.00'N, 118°13.00'E): JJV 1687. Segama valley, Sabahmas Cave, Tawau province, Sabah (05°08.52'N, 118 26.01'E): JJV 7453. Batu Baturong, N slope, Tawau province, Sabah (04°41.46'N, 118°0.45'E): JJV 7583. Segama valley, N end of limestone ridge on East bank Tabin River, Sandakan province, Sabah (05°18.49'N, 118°44.39'E): JJV 7755. Tabin Wildlife Reserve, Lahad Datu, Sabah: BOR/MOL 12, BOR/MOL 13. Limestone hill on N bank Segama River, Tawau province, Sabah (05°06.01'N, 118°13.01'E): BOR/MOL 9. Sabahmas Cave, Tawau Province, Sabah (05°08.05'N, 118°26.00'E): BOR/MOL 8. Batu Baturong, Tawau Province, Sabah (04°41.04'N, 118°00.04'E): BOR/MOL 10. N end of limestone ridge on E bank Tabin River, Sandakan Province, Sabah (05°18.04'N, 118°44.03'E): BOR/MOL 11. Tomanggong Sukau, Sandakan, Sabah (05°32.01'N, 118°23.00'E): BOR/MOL 14. Sabah, Malaysia: RMNH/MOL 335369. Sabah, N. Borneo: ZMA/MOLL 315545. Materis, Kinabatangan, Sabah (05°31.38'N, 118°01.02'E): BOR/MOL 7258.

Description.

Protoconch. Colour: pale orange to orange. Sculpture: irregular sculptural shape resulted from a combination of rounded to ellipsoidal sculpture patterns. Mesh width: 1-10. Teleoconch. Colour: orange, the colour of the teleoconch always darker than the protoconch. First whorl: convex. Subsequent whorls: convex. Suture: clearly impressed. Shoulder: narrow to slightly extended. Number of whorls: 2 ¾– 3 ½. SH: 1.05-1.68 mm. SW: 0.84-1.18 mm. SI: 1.22-1.45. Shell sculpture. Radial sculpture: absent, only weak growth lines present. Spiral sculpture: present, ca. 20-25 thin and weak spiral ribs, superficially smooth, densely arranged, appearing immediately after the protoconch, distorted by growth lines. Aperture. Shape: rounded to slightly ovoid, straight to concave parietal side, palatal edge partially contiguous with the body whorl and the parietal side, basal side convex. AH: 0.48- 0.66 mm. AW: 0.50-0.74 mm. AI: 0.76-0.98.

Diagnosis.

Georissa xesta has densely arranged spiral sculpture (8-10 ribs in every 0.1 mm), unlike G. bangueyensis (4-5 ribs in every 0.1 mm), which has more space in between the spiral ribs. The shell of G. xesta looks superficially smooth under a stereomicroscope at low contrast with less than × 20 magnification. The dense spiral sculpture is similar to the spiral ribbing pattern of G. williamsi , but the shell habitus of these two species is entirely different, where G. williamsi has a broad ultimate whorl but G. xesta does not. Based on the shell shape, G. xesta is similar to G. similis and G. corrugata , but both of these species have strongly raised radial sculpture.

Distribution.

Georissa xesta is widely distributed in Sabah, especially in the coastal areas around Kudat, Sandakan, Lahad Datu, and Tawau.

Molecular analysis.

In the ML and Bayesian analyses of G. xesta (16S: n = 2; CO1: n = 3), the Materis and Ulu Resang populations form highly supported clades 96% BS and 100% PP, which are paraphyletic with respect to G. nephrostoma .

Discussion.

The type series of G. xesta from NHMUK seems to be partially eroded. However, the densely arranged thin spiral sculpture which is the diagnostic character of the species is still visible in the type series.