Few animals match the harlequin shrimp (Hymenocera picta) for charismatic coloration and behavior. Like many shrimp, they often live in pairs. There is debate as to whether there is a second species, Hymenocera elegans; painted ("picta") or elegant ("elegans"), the Latin names seem appropriate. "Harlequin" is an archaic term for a type of clown, in reference to their festive coloring and ornamentation.
Despite this comical name, if you are a sea star, they are no joking matter. Harlequin shrimp are unrelenting predators. Their wide, flat claws are modified to act as spatulae and are use to pinch and pry off the tube feet of starfish, so they can abscond with their prey to a protected location. One of their preferred prey, the blue starfish Linckia laevigata, are too large to abduct whole, so they will feed on a small portion of the whole starfish or simply amputate a "leg" and make away with the separated limb. Even the formidable coral-consuming crown of thorns starfish (Acanthaster planci) has been know to fall prey to these killer clowns.
As I am striving to provide a science-minded resource, I should emphatically point out that their ecology and behavior should not be interpreted through a human sense of morality or propriety...harlequin shrimp, like all living creatures, are their own embodiments of a pinnacle of evolutionary success. Millenia of struggle for adaptive and reproductive success have produced an evolutionary solution in the harlequin shrimp that -- whether we admire it for its beauty or condemn it for it's predatory tactics -- has earned it a lasting role on the stage of reef ecology.