The crown-of-thorns starfish receives its name from venomous thornlike spines that cover its upper surface, resembling the biblical crown of thorns.

Its special traits, however, include being disc-shaped, multiple-armed, flexible, prehensile, heavily spined, and having a large ratio of stomach surface to body mass.

[7] The long, sharp spines on the sides of the starfish's arms and upper (aboral) surface resemble thorns and create a crown-like shape, giving the creature its name.

Recently, paleontologist Daniel Blake concluded from comparative morphology studies of A. planci that it has strong similarities with various members of the Oreasteridae.

[10] He attributed Acanthaster morphology as possibly evolving in association with its locomotion over irregular coral surfaces in higher energy environments.

Later, Carl Linnaeus described it as Asterias planci based on an illustration by Plancus and Gualtieri (1743), when he introduced his system of binomial nomenclature.

Most of these names arose from confusion in the historical literature, but Acanthaster ellisii came to be used for the distinctive starfish in the eastern Pacific Gulf of California.

The eastern Pacific Acanthaster is very distinctive (see image to the right) with its rather 'plump' body, large disk to total diameter ratio, and short, blunt spines.

In view of the level of macrogeographic homogeneity, significant allele frequency differences were observed between adjacent populations separated by about 10 km.

[12] In a very comprehensive geographic study, Benzie examined allozyme loci variation in 20 populations of A. planci, throughout the Pacific and Indian Oceans.

[2] They have detergent-like properties, and keeping starfish in limited water volumes with aeration results in large amounts of foam at the surface.

The adult crown-of-thorns is a corallivorous predator that usually preys on reef scleractinian coral polyps, as well as encrusting sessile invertebrates and dead animals.

[21][22] It climbs onto a section of living coral colony using the large number of tube feet, which lie in distinct ambulacral grooves on the oral surface.

The elongated, sharp spines covering nearly the entire upper surface of the crown-of-thorns serve as a mechanical defense against large predators.

In Northern Hemisphere coral reefs, however, crown-of-thorns populations reproduce in April and May,[46] and were also observed spawning in the Gulf of Thailand in September.

They extend their stomach over the surface of the encrusting algae and digest the tissue, as in the feeding by larger crown-of-thorns starfish on hard corals.

Most coral-feeding organisms only cause tissue loss or localized injuries, but adults of A. planci can kill entire coral colonies.

[42] Some ecologists suggest that the starfish has an important and active role in maintaining coral reef biodiversity, driving ecological succession.

Animals that depend directly or indirectly on hard corals, e.g. for shelter and food, should lose out, and herbivores and less specialist feeders gain.

[69][70] The Australian and Queensland governments funded research and set up advisory committees during the period of great anxiety about the nature of the starfish outbreaks on the GBR.

About 20 million eggs from a female spawning, having a survival rate around 0.00001% throughout development, would replace two adult starfish in a low-density population where the larvae recruit.

If, however, the survival rate increases to 0.1% (one in a thousand) throughout development from one spawning of 20 million eggs, this would result in 20,000 adult starfish where the larvae have recruited.

[51] However, abundance and species of the particular component of phytoplankton (unicellular flagellates) on which the larvae feed has a profound effect on survival and rate of growth.

[84] He suggested that runoff from such heavy rainfall may stimulate phytoplankton blooms of sufficient size to produce enough food for the larvae of A. planci through input of nutrients.

[90] Historic records of distribution patterns and numbers, though, are hard to come by, as SCUBA technology, necessary to conduct population censuses, had only been developed in the previous few decades.

To prevent overpopulation of crown-of-thorns causing widespread destruction to coral reef habitats, humans have implemented a variety of control measures.

A 2015 study by James Cook University showed that common household vinegar is also effective, as the acidity causes the starfish to disintegrate within days.

Blisters on the dorsal integument broke through the skin surface and resulted in large, open sores that exposed the internal organs.

[95] The COTSbot, which has a neural net-aided vision system, is designed to seek out crown-of-thorns starfish and give them a lethal injection of bile salts.

Field trials of the robot have begun in Moreton Bay in Brisbane to refine its navigation system, according to Queensland University of Technology researcher Matthew Dunbabin.