The crown-of-thorns starfish is one of the largest sea stars in the world. Adult's are between 25 to 35 cm and they have up to 21 arms. Its upper surface is covered with venomous thorn-like spines.

It feeds on coral reef polyps by climbing on a living colony. It will turn its stomach outward through the mouth against the healthy coral. It will digest it by excreting enzymes that cause the coral to become a soupy mixture. It absorbs the coral soup through its stomach wall. After the starfish is finished this area of coral is dead, leaving a bleached white stain as a reminder. 
An individual starfish can consume up to 6 square meters of living coral reef per year. According to research by the Australian Institue of Marine Science the crown-of-thorns starfish is responsible for the killing of almost 25% of the coral on the Great Barrier Reef since the 1980's.

The crown-of-thorns starfish only hashas a few predators. One of the main predators is the Triton's trumpet, a sea snail which growns up to 60 cm.

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