Meet two tiny new species of “vampire crabs” from Java, Indonesia! One has gorgeous purple claws, the other has stunning orange nippers, and they both have intense yellow eyes that give them their vampiric appearance. While new to science, both species have been in the aquarium trade for many years already.
In the last decade or so, colorful land-dwelling crabs from the genus Geosesarma have been sold in Asia and Europe and exported around the world. The two most popular of these vampire crabs are the violet ones and the bright orange ones, but where they originated has been a bit of a mystery: Dealers have claimed that they come from Sulawesi, Java, Krakatau, or Riau Islands in Indonesia.
Now, a trio of researchers led by Peter Ng of National University of Singapore have established that the two species are, in fact, native to central Java. The new crabs were found along hillstreams about 10 kilometers (6 miles) from each other, and the team have named the purple one Geosesarma dennerle and the orange one Geosesarma hagen. They’re described in the current volume of Raffles Bulletin of Zoology [pdf].
Adult Geosesarma dennerle are about 14 millimeters wide, and in addition to their beautifully bright purple claws (called chelae), they also have violet to purplish-brown coloration on their walking legs and on the front of their upper shell (or carapace). The rear end of their carapace is cream to yellowish-white, and their eyes are bright yellow. They live under and between rocks among vegetation on the slopes of a small valley, eating grasshoppers, larvae, and plant detritus. They’re named after the German company Dennerle, which supported the work.
The carnivorous Geosesarma hagen feeds on insects living on the ground in the dense bottom vegetation. The adults are about 13 millimeters wide, and they have bright reddish-orange chelae and similarly glowing yellow eyes. The rest of the body is mostly dark brown, though the extent of the bright orange on their backs varies a lot, with some crabs being almost completely orange. These were found along trickles of water on a banana and rubber plantation on the side of a small hill. They were named after the Rolf C. Hagen Group of Companies, a major pet supplies company in Germany that supported the work.
Though juveniles tend to be closer to the waterline, both crabs are fully terrestrial—which could explain their vibrant hues. On land, "visual communication becomes much more important," study co-author Christoph Schubart of Regensburg University tells National Geographic. "There's much more emphasis on color and visual cues rather than chemical cues, as used in the water."
Researchers already know about four Geosesarma species from Java, and with the new crabs, there are 53 members of the genus total. "Dealers working in Southeast Asia and other parts of the world know what their clients are looking for in terms of colors," Schubart says. "They start collecting in areas where scientists may not have made any expeditions so far, and suddenly the market is formed with some animals that no one has ever given a name.” Study co-author Christian Lukhaup, a professional aquarist, adds: "There were a lot of false rumors because people don't want other collectors to go there.”
Images: Chris Lukhaup (top & middle right), Tan Heok Hui (middle left), Oliver Mengedoht (bottom) via P. K. L. Ng et al., 2015