Crown-of-thorns Starfish - Physical Description

Physical Description

The body form of the crown-of-thorns starfish is fundamentally the same as that of a typical starfish. Its special traits, however, include being disc-shaped, multi-armed, flexible, prehensile and heavily spined, and having a large ratio of stomach surface to body mass. Its prehensile ability arises from the two rows of numerous tube feet that extend to the tip of each arm. In being multi-armed it has lost the five-fold symmetry (pentamerism) typical of starfish although it begins with this symmetry in its life cycle.

Adult crown-of-thorns starfish normally range in size from 25 to 35 cm (9.8 to 14 in). They have up to 21 arms. They are usually of subdued colours, pale brown to grey-green, but they may be more brightly coloured in some parts of their wide distribution.

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. The spines are stiff and very sharp and readily pierce through soft surfaces (below). Despite the battery of sharp spines on the aboral surface and blunt spines on the oral surface, the crown-of-thorns starfish's general body surface is membranous and soft. Field collection without damaging them requires careful handling with something like a blunt rod. When the starfish are removed from the water, the body surface ruptures and the body fluid leaks out so that the body collapses and flattens. The spines bend over and flatten, and the starfish becomes a sorry sight. They recover their shape when re-immersed if not left out of water to die. Handling the starfish in an aquarium system during experiments was done carefully by hand under the oral surface.