Acanthaster planci (Crown of thorns)


Large starfish with a large number of arms (up to 21), covered in (poisonous) spines. Olive till dark green or rusty brown.


Common in small numbers on any reef. When seen in large numbers they can form a serious threat to the corals on the reef.


From the Red Sea westwards till Mexico. On coral reefs in a depth range of 1-30 meters.


Gonads increase in size as the animals become sexually mature and at maturity fill the arms and extend into the disk region. Females have been reported to have more than 20% body mass consisting of gonads. This high percentage explains how these starfish can reproduce so quickly. In the southern hemisphere starfish spawn in december/january, in the northern hemisphere this takes place in april/may. The fertilized eggs develop into larvae, and they take up to 5-7 months to grow into a full-grown starfish.


Up to 50cm.

Prey / Predation

It feeds on hard corals, which it eats by injecting a substance containing enzymes inside the coral that dissolves the coral, and then sucking up the soft tissue. It can extrude a big part of its stomach to suck up its food. It also has natural predators, other then divers taking them away from reefs, being some species of pufferfish and the Triton mollusk.

Special features

They are often seen as a plague, although in small numbers they exist in almost every coral reef.