i would have to go with pistol shrimp. although not the biggest or meanest they are a neat little animal and when paired with a goby put on a great show maintaining there burrow.
they are also the only known animal that can create light. the snapping sound is actually a cavatation bubble that colapses so quickly it heats to 5000-2000 k and creates a small amount of ultraviolet light. google sonoluminescence if u dont belive me