Georissa saulae (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 saulae (van Benthem-Jutting, 1966)

Hydrocena saulae van Benthem-Jutting, 1966: 40, fig. 2; Saul 1967: 109.

Georissa saulae (van Benthem-Jutting): Thompson and Dance 1983: 118, fig. 29, 53-54; Haase and Schilthuizen 2007: 217, fig. 2; Clements 2008: 2762; Schilthuizen et al. 2012: 278; Beron 2015: 181; Phung et al. 2017: 68, fig. 8; Osikowski et al. 2017: 80.

Type locality.

Malaysia, Borneo, Sabah, Laying cave, Keningau.

Type material.

Holotype. Malaysia, Borneo, Sabah, Laying cave, Keningau: ZMA/MOLL 135731 (seen). Paratypes. Malaysia, Borneo, Sabah, Laying cave, Keningau: ZMA/MOLL 135598 (seen), ZMA/MOLL 135599 (seen).

Other material.

Simbaluyon limestone hill, Sabah, Malaysia: RMNH/MOL 333913, RMNH/MOL 333919. Crocker Range National Park, Gua Laing, Keningau, Sabah (05°29.00'N, 116°08.00'E): RMNH/MOL 335180, ZMA/MOLL 315592, ZMA/MOLL 315593, JJV 1119. Sepulut Valley, Gua Pungiton, Sabah (04°42.41'N, 116°36.04'E): BOR/MOL 28, BOR/MOL 12770, JJV 7544. Sepulut valley, Gua Sanaron, Sabah (04°42.05'N, 116°36.01'E): BOR/MOL 29, BOR/MOL 32, BOR/MOL 3493, JJV 7660. Pinangah valley, Batu Urun (Bukit Sinobang), Sabah (04°48.40'N, 116°37.35'E): BOR/MOL 31, JJV 1144, JJV 5632, JJV 7993. Mahua, Sabah: BOR/MOL 33. Pun Batu, Sepulut, Sabah (04°45.00'N, 116°10.00'E): JJV 1268. Sepulut valley, Batu Punggul, Sabah: JJV 1904.

Description.

Protoconch. Color: red to brown. Sculpture: meshed - ellipsoidal mesh pattern. Mesh width: 29-54 µm. Teleoconch. Color: brown to red. First whorl: convex to rounded. Subsequent whorls: convex to rounded. SH: 1.32-1.86 mm, SW: 1.14-1.48 mm, SI: 1.12-1.26. Total number of whorls: 2 ½ -3 ¼. Shell sculpture. Radial sculpture: often present, when formed by vertical connections between corresponding scales on successive spiral ribs. These vertical connections, especially on the first whorls, form evenly spaced ribs that are raised when crossing a spiral rib. Spiral sculpture: present at the early teleoconch, subsequently becoming weaker, and later only short discontinuous lines are visible in between the radial sculptures. Scales: usually three or four discontinuous series of vertical, low to high-projecting scales, broad to pointed (only if the spiral series of scales are discontinuous). Aperture. Shape: rounded to slightly oval. Basal side: rounded, slightly angular before the columellar region. Parietal side: straight, connected to the palatal edge. AH: 0.58-0.83 mm, AW: 0.70-0.94 mm, AI: 0.76-0.92. Holotype dimension. SH: 1.60 mm, SW: 1.28 mm, AH: 0.66 mm, AW: 0.80 mm.

Cross diagnosis.

Georissa saulae possesses clear diagnostic shell characters for distinction from other “scaly” Georissa species. G. saulae lacks a clear formation of spiral ribbing: although the spiral arrangement of the scales gives the impression of spiral sculpture, no underlying ribs are discernable. G. scalinella , G. kinabatanganensis , and G. hosei , on the other hand, have clear diagnostic spiral ribs. The shell whorls of G. saulae are broad but not as rapidly expanding as in G. hosei , G. scalinella or G. kinabatanganensis . It can also be distinguished from G. scalinella and G. hosei on the basis of a more elongate-conical shell shape and the aperture shape that is more rounded rather than oval.

Distribution.

The type locality of Georissa saulae is Laying cave, in the Crocker Range, Keningau, Sabah (a misspelling of Laing cave). Otherwise known from limestone outcrops in Sabah’s interior, viz., Simbaluyon, Sinobang, Sanaron, and Pungiton, and also has been recorded from Mahua, Sabah, which is not a limestone area. Phung et al. (2017) also report it from Pulau Tiga, Sabah.

Molecular analysis.

ML and Bayesian analyses show Georissa saulae (16S: n = 11) as a monophyletic group with 100% BS and 100% PP. Schilthuizen et al. (2012) reported that G. saulae is a paraphyletic group from which emerges the cave-dwelling species G. filiasaulae ( Haase and Schilthuizen 2007), a fully unsculptured species that was not included in the present study. G. saulae + G. filiasaulae are sister to all other species in the "scaly group" (unpublished data).

Discussion.

Georissa saulae was initially described as Hydrocena saulae van Benthem-Jutting, 1966, then assigned to the genus Georissa by Thompson and Dance (1983). Thompson and Dance (1983) compared G. saulae with G. scalinella , and even suggested G. saulae might be a subspecies. In contrast, we find that G. saulae is a proper species with very distinct conchological characters, especially the presence of radial ribs on the shell, which makes it easy to identify. In some specimens from the entrance of the Batu Sanaron cave system, the vertical scales are spaced, and radial sculpture is weak. Such individuals presumably represent the hybrid zone with the cave-dwelling G. filiasaulae ( Haase and Schilthuizen 2007, Schilthuizen et al. 2012).