Crown-of-thorns starfish substrates with their arms and, when offered a choice of substrates, tend to settle on coralline algae, which they will subsequently feed on. In the classic pattern for echinoderms, the bilaterally symmetrical larva is replaced by a pentamerously symmetrical stage at metamorphosis, with the latter's body axis bearing no relationship to that of the larva. Thus the newly metamorphosed starfish are five-armed and are 0.4–1 mm diameter. (Note the size of the tube feet relative to the size of the animal.) They feed on the thin coating layers of hard encrusting algae (coralline algae) on the undersides of dead coral
Crown-of-thorns starfish of a proportion of individuals with regenerating arms. A variety of about 11 species have been reported to prey occasionally on uninjured and healthy adults of "A. planci". All of these are generalist feeders and none of these, however, seems to specifically prefer the starfish as a food source. This number, however, is probably lower, as some of these presumed predators have not been witnessed reliably in the field. Some of those witnessed are: Gonads increase in size as the animals become sexually mature and at maturity fill the arms and extend into the disk region. The ripe ovaries and