Crown of Thorns Starfish

This is a Crown of Thorns Starfish or Acanthaster planci. It is considered to be a pest. Here is a short explanation about this animal from Wikipedia.

The crown-of-thorns starfish, 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 thorn-like 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 in 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 this region.

Usually, these starfish are brightly colored, but this is a museum specimen in the Smithsonian Natural History Museum.