active animal animals aquatic closeup crab crustaceans decapod exoskeleton gregarious India macro marine nocturnal crabs pincers Sand bubbler crabs sand-bubblers Scopimera abstract art artwork background ball beach branch branching bubble crab coast construction crustacea details dotilla dotillidae environment feed food foraging grain hole intelligence life little marble marbles memory nature network ocean pattern process art radial sand sandy sea shore sphere spheres structure symmetry texture wildlife bubble Camouflage critter hide hiding