In Río Hitoy, there is a peculiar shrimp.  It seems to inhabit cobble-dominated, high current velocity, areas of the river.  I don’t know what it is or what it does, but it’s chelae are modified into large, hook-like structures.

UPDATE:  I found a paper describing shrimp found in Boca Del Toro, Panama, which is pretty close to Hitoy.  I had asked a friend, Bernald, which family of tropical shrimp may not have chelae (pinchers), and he suggested Atyidae.  The paper describes Atyids, including Atya scabra, which is widely distributed (Aftrica to Panama) and looks similar to this species… so, we’ll call it Atya scabra…