Infra-order Brachyura, Superfamily Grapsoidae, Family Varunidae
Freshwater crab | Ptychognathus pusillus Heller, 1865
A small crab with up to 25 mm wide carapace. The top of the carapace is a speckled and the base color varies depending on the substratum the crab is found in. Male crabs of this species have a characteristic tuft of fine brown hairs on the outside of each claw. Females have smaller claws that are free of hairs.
The so-called freshwater crab of Christmas Island actually prefers brackish water and usually lives near the sea. It needs to return to the sea to release its eggs.
Read more about Christmas Island's freshwater crab in the book
"Crabs of Christmas Island" by Max Orchard