A sponge crab.   These crabs use sponges or tunicates for camouflage,

and this one is carrying a colonial tunicate .

(Edithburgh, South Australia)

arthropod; crustacean; decapod; true crab; sponge crab; Arthropoda; subP Crustacea; Malacostraca; Decapoda; subOrder Pleocyemata; infraOrder Brachyura; superFamily Dromioidea; Dromiidae; Austrodromidia octodentata; 

with Leach's colonial tunicate; Chordata; subP Urochordata; Ascidiacea; Pleurogona; Botryllidae; Botrylloides leachi, Australia