A Crab That I Saw At Thelagamu Oya

This is the only critter I had a chance to observe in our recent trip to Knuckles.  Could any of you help me to identify this one?

A Short Trip In Knuckles Conservation Forest, Riversturn, Pitawala Pathana And Thelagamu Oya

This is from our(my family and some of my workmates') trip to The Reversturn Peak of Knuckles mountain range on 06/06/2010.  We visited Reversturn, Pitawala pathana grassland, and Thelagamu Oya river, all within the premises of Knuckles conservation forest, which is mainly highland rain-forest, with relatively short trees, less underbrush and hardly any canopy.   As we had to make it a short one day trip, we didn't have much of a chance observing or studying its wildlife. My attempts to gather some info online have so far been fruitless. More images and video are available on my travel blog.