The crown-of-thorns starfish (frequently abbreviated to COTS), Acanthaster planci, is a large starfish that preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from venomous thornlike spines that cover its upper surface, resembling the biblical crown of thorns. It is one of the largest starfish in the world.

A. planci has a very wide Indo-Pacific distribution. It is perhaps most common around Australia, but can occur at tropical and subtropical latitudes from the Red Sea and the East African coast across the Indian Ocean, and across the Pacific Ocean to the west coast of Central America. It occurs where coral reefs or hard coral communities occur in the region.

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