[Crustacea • 2026] Geosesarma penrissen • A New Species of Vampire Crab of the Genus Geosesarma De Man, 1892 (Brachyura: Sesarmidae) from A montane forest in southwestern Sarawak, Malaysian Borneo

 

Geosesarma penrissen

Grinang, P. Y. C. Ng & P. K. L. Ng, 2026 

 

The Raffles Bulletin of Zoology. 74; 

Abstract 

 A new species of semiterrestrial crab, Geosesarma penrissen, new species, is described herein from Mount Penrissen in southwestern Sarawak, Malaysia. It represents the third species of Geosesarma known from the montane forests of Borneo, the other two being G. larsi Ng & Grinang, 2018 from Mount Ampungan in Serian, Sarawak, and G. aurantium Ng, 1995 from Mount Silam in Sabah. Diagnostic characters distinguishing G. penrissen, new species, from its congeners are provided, together with ecological notes on its highland habitat. 

Key words. freshwater crab, semiterrestrial, taxonomy, lowland forest, comparative morphology

Geosesarma penrissen, new species, live colouration.
A–C, holotype male (10.6 × 10.2 mm) (ZRC 2024.0567); D, paratype male (10.7 × 10.5 mm) (ZRC 2024.0171); E, adult male, on shrub, Batu Panggah trail, photographed 2311 hrs; 6 July 2023 (not collected); F, subadult, on shrub, Batu Panggah trail, photographed 2118 hrs, 6 July 2023 (not collected).

All specimens from Sarawak. E, F, photographed by Chien Lee.

 Geosesarma penrissen, new species

Diagnosis. Carapace almost square, width-to-length ratio 1.01–1.07, lateral margins gently sinuous, subparallel (Figs. 1A, D, 2A–D, 5A, C, F, 6A, D); dorsal surface with welldefined regions, anterior regions covered with small, rounded or flattened, squamate granules (Figs. 1A, C, E, F, 2A–D, 5A, C, E, 6A, D); front deflexed, with 2 broad subtruncate lobes, separated by shallow median concavity; postfrontal, protogastric lobe prominent, sharp-edged (Figs. 1A, C, D, 2A–D, 3A, 6C, F); external orbital tooth acutely triangular, outer margins curving anteriorly, tooth directed obliquely and laterally, clearly extending beyond lateral margin of carapace (Figs. 2A–D, 5A, C, E, 6A, D). Merus of third maxilliped ...

JONGKAR GRINANG, PAUL Y. C. NG and PETER K. L. NG. 2026. A New Species of Vampire Crab of the Genus Geosesarma De Man, 1892 (Crustacea: Brachyura: Sesarmidae) from A montane forest in southwestern Sarawak, Malaysian Borneo. The Raffles Bulletin of Zoology. 74; 457–464.