Geosesarma batak & Geosesarma tagbanua: Two new species of semi-terrestrial Sesarmid Crabs from Palawan Island, Philippines.

Sesarmid Crabs of the genus Geosesarma are found from India and Southeast Asia and the islands of the western Pacific as far east as Hawaii and the Solomons. They are terrestrial of freshwater-dwelling, with egss laid on land; the larvae develop past the free-swiming aquatic stage in the eggs and are similar to the adults when they emerge.

In a paper published in the Raffles Bulletin of Zoology on 9 November 2016, Marivene Manuel-Santos of the Zoology Division at the National Museum of the Philippines, Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore , and Hendrik Freitag of the Biology Department at Ateneo de Manila University, describe two new species of Geosesarma from Palawan Island in the Philippines.

The first new species described is named Geosesarma batak, where 'batak' refers to the Batak people who are indigenous to northeastern Palawan and considered to be the oldest indigenous group in the Philippines. These Crabs have a squarish carapace with the largest male specimen measuring 22.8 by 22.4 mm. They are brown in colour with red and yellow markings. They were found living in forests close to streams, but seldom on the ground, apparently prefering to live in knotholes on trees.

Geosesarma batak, female (20.6 × 20.1 mm), Concepcion, Taranaban River. Manuel-Santos et al. (2016).

The second new species is named Geosesarma tagbanua, after the indigenous Tagbanua people of central and northern Palawan. This species also has a squarish carapace, with the largest male specimen found measuring 21.8 by 21.8 mm. They were found living in a limestone cave and a montane forest in an area with large boulders.

Geosesarma tagbanua, male (21.8 × 21.8 mm), Lipuun Point, Tabon Caves. Manuel-Santos et al. (2016).

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Two new species of Vampire Crabs from Central Java.

Sesarmid crabs of the genus Geosesarma are large, often colourful, fully terrestrial Crabs found in Southeast Asia and Indonesia. In recent years they have been traded in the international aquarium trade under the name ‘Vampire Crabs’ (which is fanciful, the Crabs do not drink blood but feed largely on small Insects etc.), with several species unknown to science appearing in the aquarium trade. The origin of these has been hard to track down, with dealers claiming they originate from Sulawesi, Java, Krakatau (highly unlikely since Krakatau is an active volcanic island with no fresh water supply, which has been completely resettled by wildlife from outside following the destruction of the island by a violent eruption in the late nineteenth century, and its subsequent re-appearance) or the Riau Islands.

In a paper published in the Raffles Bulletin of Zoology on 16 January 2015 Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore, Christoph Schubart of Zoology and Evolutionary Biology at Universität Regensburg and Christian Lukhaup of Bittenfeld in Germany describe two new species of Vampire Crabs from Central Java, both of which have previously been encountered in the aquarium trade.

The first new specie described is named Geosesarma dennerle, in honour of the German company Dennerle, who supported Christian Lukhaup’s studies in Java. The Crabs have squarish bodies, a little wider than long, with the largest male located having a carapace 14.4 by 14.0 mm and the largest female 13.5 by 11.8 mm. They have a very distinctive colouration, with the front half of the carapace and legs being violet or purple and the rear of the carapace being cream or yellowish white. The crabs were found living on the slopes of a small valley, between rocks and in dense vegetation. The species has also been found being traded in Germany under the names ‘Vampir Vampirkrabbe’ and ‘Blaue Vampirkrabbe’.

Specimens of Geosesarma dennerle from Cilacap on Java. Christian Lukhaup in Ng et al. (2015).

The second new species described is named Geosesarma hagen, in honour of the Rolf C. Hagen Group of Companies, who are a major pet supplies group in Germany, and who supported both Christian Lukhaup’s studies in Java and subsequent work on the Crabs by Christoph Schubart. These Crabs are also squarish and wider than they are long; the largest male found had a carapace 13.9 by 13.3 mm, while the largest female was 14.5 by 13.4 mm. This species also has very distinctive colouration, with the front of the carapace and walking legs being brown while the rear of the carapace and claws are bright orange or yellow. This species has been traded in Germany as ‘Rot Vampirkrabbe’. The Crabs were found living in a Banana and Rubber plantation on the side of a small hill, about 300 m from a road.

Specimen of Geosesarma hagen from Cilacap on Java. Christian Lukhaup in Ng et al. (2015).

Ng et al. also note that both species are apparently being heavily collected for the aquarium trade, and that local people report that they have become scarcer in recent years. This strongly implies that they are being collected in an unsustainable way, and that if this persists it will be necessary to develop a conservation management plan for these Crabs, probably involving a captive breeding program. They also note that the conservation status of land Crabs as a group has not yet been assessed under the guidelines of the International Union for the Conservation of Nature’s Red List of Threatened Species, and that this needs to be done in the near future, particularly if their popularity in the aquarium trade persists.

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