the crown-of-thorns starfish ("acanthaster planci") is a type of sea star. usually, they have orange-red to purplish skin, with yellow or pink spikes on their skin. the crown-of-thorns is also one of the largest starfish in the world, as it has a diameter of up to 3 feet. the crown-of-thorns lives in the warmer areas of the pacific ocean, indian ocean, and red sea.