beach bug crab Crustacean sand sea crab shore concrete Indian Ocean KZN Sea-Crab South Africa sunny warm crabs eat food sea seaside shell shellfish animals claw claws crab texture India krayker nature pattern pattern crab pincher sands seafood texture aquatic crab on the sands animal closeup coast creature exoskeleton Hermit Crab hide macro marine scavengers sea snail shell social big blue fake ocean stone wall water clam seaweed shells starfish summer