active animal animals aquatic closeup crab crustaceans decapod exoskeleton gregarious India macro marine nocturnal crabs pincers Sand bubbler crabs sand-bubblers Scopimera catch catching clawed claws color colored colors colour coloured colours crab-nets crabbing crabs creatures decapods drop-nets fishing floats food gray green grey lines mesh metal-rings nets nylon old rings rust rusted rusty seafood