Research Article |
Corresponding author: Peter K. L. Ng ( peterng@nus.edu.sg ) Academic editor: Luis Ernesto Bezerra
© 2021 Peter K. L. Ng.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ng PKL (2021) Geosesarma sodalis, a new species of vampire crab (Crustacea, Brachyura, Sesarmidae) from a limestone cave in central Sarawak, Malaysia. ZooKeys 1031: 133-141. https://doi.org/10.3897/zookeys.1031.63134
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A new species of semi-terrestrial crab of the genus Geosesarma (Sesarmidae) is described from a limestone cave in central Sarawak, Malaysian Borneo. Geosesarma sodalis sp. nov. is characterised by its quadrate carapace, absence of a flagellum on the exopod of the third maxilliped, presence of 10 or 11 sharp tubercles on the dactylus of the chela and a diagnostic male first gonopod structure. This is the sixth species of Geosesarma reported from Sarawak, and the first member of the genus collected from inside caves.
Borneo, cavernicolous, description, Geosesarma, karst, new taxon, taxonomy
In 2005, Rob Stuebing passed the author several brachyuran crabs he collected while surveying limestone caves in the Bintulu area in central Sarawak. The material included a new species of a cavernicolous gecarcinucid, and in 2006, fresh surveys were made in the caves to obtain more specimens. This new material formed the basis for the description of a new species of Arachnothelphusa Ng, 1991, by
Among the original 2005 material collected by Stuebing was a specimen of Geosesarma De Man, 1892 (Sesarmidae). Examination of the specimen showed it to be a new species, here named Geosesarma sodalis sp. nov. This is also the first record of a Geosesarma from inside caves. Geosesarma are often called vampire crabs because many species have bright yellow eyes in life (see
Measurements provided are the carapace width and length. The terminology used in this paper follows
Sesarma (Geosesarma) nodulifera De Man, 1892; subsequent designation by
Holotype: male (10.1 × 9.8 mm) (
Carapace quadrate, slightly wider than long, width to length ratio 1.03, lateral margins gently concave, subparallel (Fig.
Not known.
Not known.
The name is derived from the Latin noun for comradeship; alluding to the deep friendship the author has had over the last 30 years with the collector, Rob Stuebing, who has collected many interesting species for him.
The island of Borneo has 13 known species of Geosesarma, all of which are endemic to the island. Five species occur in the state of Sarawak (
Five of the species in this group are present in Sarawak and Brunei: G. gracillimum, G. katibas, G. bau, G. larsi, and G. sodalis sp. nov. Compared to G. gracillimum, the carapace of G. sodalis sp. nov. is more quadrate with the lateral margins subparallel (Fig.
Geosesarma sodalis sp. nov., holotype male (10.1 × 9.8 mm) (
Geosesarma sodalis sp. nov., holotype male (10.1 × 9.8 mm) (
The relatively longer fingers (distinctly longer than the palm) and the outer surface of the chela with fewer small granules in G. sodalis sp. nov. (Fig.
The male chela and G1 differences between G. sodalis sp. nov. and G. spectrum (from Brunei) are the same as for the Sarawakian G. katibas. Geosesarma sodalis sp. nov. differs markedly from the two species in this group from Indonesian Kalimantan, G. ambawang and G. pontianak, in possessing a G1 that is proportionately stouter and the subdistal part of the outer margin has a prominent right angled hump-like arch (see
Noteworthy is that G. sodalis sp. nov. was collected inside a cave where a cavernicolous species of gecarcinucid, Arachnothelphusa sarang Grinang & Ng, 2021, is present. Bukit Sarang is an isolated limestone outcrop with a complex of small caves, most of which probably have subterranean interconnections, and is part of the Tatau river basin in central Sarawak. The type specimen was obtained in moist areas several hundred meters from the cave entrance (RB Stuebing pers. comm.). Although more surveys in and around the Bukit Sarang were conducted in 2006 and more specimens of A. sarang were collected (
Geosesarma sodalis sp. nov., however, does not have prominently elongated legs or reduced eyes typical of true troglobitic taxa, and must be treated as troglophile. It is probably more widespread outside the cave habitat. The site it was collected from is several hundred metres from the cave entrance and there was no light at all. The sympatric Arachnothelphusa sarang possesses some cave-dwelling characters-there is hardly any pigmentation on the body and legs and the pereopods are elongated, but the eyes are not reduced with the cornea still distinct, with
No Geosesarma species had previously been recorded from caves, although one sesarmid genus Karstarma Davie & Ng, 2007, is known to live in or closely associated with limestone caves. Karstarma species are widely distributed in the Indo-West Pacific, with 18 recognised species (see
Another species of sesarmid which was originally desrribed from near the entrance of a cave in Myanmar, Pseudosesarma brehieri Ng, 2018, is now known to normally live in mangrove habitats (
The author is most grateful to Rob Stuebing for entrusting the material from Bukit Sarang to the author for study.