harlequins only eat starfish - there are conflicting reports on them accepting brittle stars when entirely out of other options, but it seems like if they do, it would be an extreme famine food
Also, just to clarify for anyone wondering- harlequin shrimp do not just eat the tube feet of these critters, they eat the whole critter, typically starting with the tube feet (presumably to keep the critter from fleeing/struggling while they eat).
