The upper or aboral surface is called the " exumbrella " and the lower surface is called the " subumbrella "; the mouth is located on the lower surface, which may be partially closed by a membrane extending inward from the margin ( called the " velum " ).
42.
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 . When the starfish is removed from the water, the body surface ruptures and the body fluid leaks out, so the body collapses and flattens.
