By Nneka Nwogwugwu
An expedition to the forests of Sierra Leone, West Africa, revealed two species of crabs new to science and two species not seen in more than half a century.
The research team found an Afzelius’s crab (Afrithelphusa afzelii), which has had no recorded sighting for 225 years (since 1796), and the Sierra Leone crab, not seen in 66 years.
Also found were two species of crabs belonging to the genus of the common river crab in West Africa. Only one species of this genus was known to exist in Sierra Leone before now.
The quest for crabs was sponsored by the conservation organization Re:wild, as the Sierra Leone crab is number eight on Re:wild’s 25 most-wanted lost species list. So far, their Search for Lost Species program has rediscovered seven other lost species.
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On a recent expedition to the remote forests of Sierra Leone, West Africa, researchers found two species of crabs new to science and rediscovered two species not seen in more than half a century.
For 23 days, Pierre A. Mvogo Ndongo, a researcher from the University of Douala in Cameroon, trekked through remote rainforests in search of the Sierra Leone crab (Afrithelphusa leonensis), a unique purple-clawed land crab that has not been spotted by scientists since 1955.
Ndongo asked locals during his journey if they had seen crabs that live on land, far from permanent water sources.
Two men in Moyamba district described colorful crabs living nearby and led him to a farm bordering the forest. Within three days, Mvogo Ndongo and his team found an Afzelius’s crab (Afrithelphusa afzelii), which has had no recorded sighting for 225 years (since 1796). Over the next few days, the researchers found many of the orange-legged, purple-bodied crabs in that area, indicating the presence of a healthy local population.
The team then traveled to Sugar Loaf Mountain in Western Area National Park in search of their target species, the Sierra Leone crab. The spread of COVID-19 and looming lockdowns meant that their time was limited.
“In the four days searching the dense forests on Sugar Loaf Mountain, I was able to find six specimens of the Sierra Leone crab because I was able to recruit local people to go into the forest and search with me,” Mvogo Ndongo said. His team excavated burrows using tools, working carefully not to hurt the crabs. “When I found the Sierra Leone crab, I was very, very happy. This was after almost three weeks of searching for lost species.”
African land crabs are unique; only five species are known to exist. Compared to their water-dwelling relatives, these land crabs are more colorful and live in burrows, rock crevices, and trees away from permanent water sources. They use specialized lung-like structures to breathe air, and some even climb trees.
The team also found two species of crabs previously unknown to science, in the genus Liberonautes, or the genus of the common river crab in West Africa. Only one species of this genus was known to exist in Sierra Leone before now.
Describing and naming these species will require detailed morphological examination, DNA sequence comparisons and specialist expertise, but the process is currently on hold due to COVID-19 travel restrictions.
Neil Cumberlidge, a professor at Northern Michigan University who worked with Mvogo Ndongo on the expedition says they are optimistic about finding healthy populations of both of the “lost” species of crabs.
However, the forests in which the crabs live, part of the Upper Guinea Forest block, face threats, Mongabay reports.
