The Robinson Library >> Science >> Zoology >> Phylum Echinodermata
Crown of Thorns Starfish

Acanthaster planci


The crown of thorns is so named because its entire upper surface is covered with large venomous spines. The exact nature of the venom is not fully understood, nor is it known what purpose it serves.

crown of thorns starfish

A fairly large echinoderm, the crown of thorns averages 9-14 inches across, with individuals over 27 inches in diameter being fairly common. Each of its arms (up to 21 per individual) has a light-sensitive eyespot at the tip. Individual coloration varies from red and orange to purple, and is thought to be the result of differences in diet.

Distribution and Habitat

Crown of thorns starfish are found on coral reefs throughout the Indian and Pacific oceans, but are especially common on the Great Barrier Reef.


While developing as larvae in the water column, individuals of this species consume smaller planktonic organisms. As adults, they are opportunistic carnivores, consuming reef-building corals, stony corals, and dead animals. It feeds by everting its stomach through its mouth onto its prey and digesting the tissues, absorbing the nutrients through the stomach wall. Although they are thought to be nocturnal, some larger individuals feed during the day. They generally feed alone, but during "population outbreaks" many individuals will aggregate in large groups. Such aggregates can cause extensive damage to a coral reef, damage that can take many years for the reef to recover from.

Reproduction and Development

Populations in the northern hemisphere generally spawn between May and August, while populations in the southern hemisphere spawn between November and February.

A single female can produce up to 60 million eggs in a breeding season, which she releases into the water column to be fertilized by males' sperm. Larvae typically spend between two and four weeks drifting in ocean currents and feeding on phytoplankton. They then settle on shallow reefs, eventually becoming five-armed juvenile starfish which feed on coralline algae. They begin to feed on corals at four to six months, and are sexually mature after two years, by which time all 21 of their arms have fully developed.

Scientific Classification

phylum Echinodermata
class Asteroidea
order Spinulosida
family Acanthasteridae
genus & species Acanthaster planci

Animal Diversity Web

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This page was last updated on 06/14/2017.