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
Starfish are simultaneous hermaphrodites, producing eggs and sperm at the same time and in a few of these, the same gonad, called an ovotestis, produces both eggs and sperm. Other starfish are sequential hermaphrodites. Protandrous individuals of species like "Asterina gibbosa" start life as males before changing sex into females as they grow older. In some species such as "Nepanthia belcheri", a large female can split in half and the resulting offspring are males. When these grow large enough they change back into females. Each starfish arm contains two gonads that release gametes through openings called gonoducts, located on the central