Infra-order Brachyura, Superfamily Grapsoidea, Family Sesarmidae
Jackson's crab | Karstarma Jacksoni (Balss,1934)
A small crab with a flat, smooth dark red to purple carapace up to 25 mm wide. Dark red eyes. Long spidery legs. Pink to cream claws.
Jackson’s crab was first described from specimens collected at Christmas Island. Not known from anywhere else. Has been previously known under the name Sesarma jacksoni but recent studies have led to it being re-assigned to the genus Karstarma.
Prefers moist, cool environments on the lower terraces and caves from sea level to 50 metres above sea level.
Read more about Christmas Island's Jackson's crab in the book
"Crabs of Christmas Island" by Max Orchard