A new genus and species of oreasterid, Astrosarkus idipi (Asteroidea, Echinodermata) is described from the central Pacific and southern Indian Oceans. The new taxon is characterized by strong reduction and modification of the endoskeleton. Only the terminals and adambulacral spine and mouth-angle spines are externally expressed. The body wall is composed mostly of a thick, smooth flesh that obscures the abactinal, actinal, and marginal plates. The fleshy layer contains an extensive system of channels that begin in the coelom and terminate at the body surface. Also unique is the internal expression of fixed, spiny processes on the ambulacral plates within the coelom. The novel body form of Astrosarkus, parallel to the very different morphology of Acanthaster, demonstrates the morphological plasticity within the Oreasteracea and the conservative evolution of the axially derived ambulacral skeleton.