Georissa hadra Thompson & Dance, 1983

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

publication ID

publication LSID

persistent identifier

treatment provided by

ZooKeys by Pensoft

scientific name

Georissa hadra Thompson & Dance, 1983


Georissa hadra Thompson & Dance, 1983 

Georissa hadra  Thompson & Dance, 1983: 115-116, fig. 32, 43-46.

Type locality.

Butik Besungai, a small limestone hill 0.5 miles southwest of Batu Gading, and about 4 miles northeast of Long Lama, Baram Valley, Fourth Division, Sarawak. 03°52'N, 114°25'E.

Type material.

Holotype. Butik Besungai, a small limestone hill 0.5 miles southwest of Batu Gading, and about 4 miles northeast of Long Lama, Baram Valley, Fourth Division, Sarawak: UF36107 (not seen). Paratypes. Butik Besungai ½ mile SW. of Batu Gading, 4 miles NE. of Long Lama, Baram Valley, 4th Div., Sarawak, Malaysia: BMNH 1984004 (seen). Baram valley, Long Lama, Bt. Besungai 0.5 m SW of Batu Gading, Sarawak (03°52.00'N, 114°25.00'E): JJV 13421 (seen).

Other material.

Lang Cave, Mulu N.P., Mulu, Sarawak (04°01.49'N, 114°49.48'E): MZU/MOL 17.32, MZU/MOL 17.33, MZU/MOL 17.34, MZU/MOL 17.35. Deer Cave, Mulu N.P., Mulu, Sarawak: JJV 10533 (this sample, approximately 120 individuals, also contains G. muluensis  ), JJV 10554 (5 individual of G. muluensis  , 1 individual G. hadra  ), JJV 10533 (this sample, approximately 150 individuals, also contains G. muluensis  and G. kobelti  ).

Butik = a misspelling of Bukit, a local name for hill.


Protoconch. Color: orange. Sculpture pattern: meshed - rounded to ellipsoidal or undefined mesh shape. Mesh width: 12-24 µm. Teleoconch. Color: orange. First whorl: with a distinct shoulder (provided with a series of minuscule scales), above the shoulder flat and tapering towards the suture, below the shoulder flat and cylindrical. Subsequent whorls: distinctly scalariform, with three separate aspects separated by two or more main spiral series of scales: above the uppermost spiral series gently curved towards the suture; in between both spiral series flat and cylindrical; below the lowest spiral series abruptly narrowed towards the deeply impressed suture (on the final whorl these three aspects fuse, forming a uniformly rounded impression). SH: 2.61-2.91 mm, SW: 2.05-2.19 mm, SI: 1.21-1.37. Total number of whorls: 2 ¾ -3 ¼. Shell sculpture. Radial sculpture: absent, but with strong and unevenly layered growth lines. Spiral sculpture: present, weakly sculpted, continuous to discontinuous. Scales: two to four irregularly spaced series of low to high, and minute to broad diagonal scales, densely spaced, the first scale series always the strongest, weaker series appearing later at the spire. Aperture. Shape: rounded, with a tilt below the palatal side. Basal side: rounded, angular at the columellar region. Parietal side: straight to curved. AH: 1.11-1.33 mm, AW: 1.32-1.48 mm, AI: 0.83-1.01.

Cross diagnosis.

Georissa hadra  has scales which are densely arranged, unlike G. scalinella  , G. hosei  , G. muluensis  , G. anyiensis  , and G. kobelti  , which have more widely spaced scales. In shell shape, G. hadra  is similar to the later three species but larger and more distinctly scalariform. G. hadra  is similar in size to G. niahensis  , but it has a more slender habitus and a more rounded periphery.


The type locality for G. hadra  is Bukit Besungai, Baram, Sarawak. We also obtained it at Mulu, Sarawak. Currently, therefore, the known distribution range is restricted to Mulu and Baram.

Molecular analysis.

ML and Bayesian analyses retrieve G. hadra  (16S: n = 4; CO1: n = 4) as a single clade with 89% BS and 100% PP, sister to G. muluensis  .


The paratypes of Thompson and Dance (1983) have a very pale orange color, compared to recently collected materials from Mulu; presumably the color has faded.