Abstract
Terpios hoshinota Rützler & Muzik, 1993 is a poriferan species that competes with corals and is known as a coral-killing sponge. However, limited information is available on its biology, including morphological traits. This study aims to examine the arrangement and development of spicules in various body parts of the sponge, including settled larvae. Spicules were found to appear on the second day after settlement and were present in all individuals on the fifth day. The spicules in the thread-like tissue of the growth portion were oriented in the direction of growth, with their pointed tips facing forward to support the elongated pioneer tissue. Furthermore, the spicules in the surface layer of the sponge tissue were perpendicular, with outward-facing tips associated with collagens. The study indicates that the spicules of T. hoshinota are arranged to support both encrusting basal tissue and pioneering tissue to colonize corals.