ABSTRACT
Thandar (1989) recently described Neothyonidium arthroprocessum, a new species of a phyllophorid holothurian from South Africa, based on two specimens (holotype: female; paratype: male) taken from False Bay, east of the Cape Peninsula. The species is peculiar in several respects. It has 20 tentacles in two rings of 10 + 10, but the inner ring is small and lies deep within the oral cavity. In the holotype there are four series of narrow transverse slits in the body wall of the dorso-lateral and ventral interradii. The calcareous ring is tubular, with only the radial plates prolonged into bifurcate processes but each process is linked with the adjacent process of the neighbouring radial plate. Both respiratory trees are remarkable, each giving off at about mid-body, a short transverse branch which passes medially and subdivides into two additional branches. Since the trees lie in the dorso-lateral and ventral interradii some of their end branches are in close contact or communication with the transverse slits. Histological examination of the body wall reveals this communication and indicates that there are two types of end branches. However, the significance of this is not yet understood. The body wall spicules are exclusively in the form of fairly stout perforated rods, but the introvert possesses also tables, of the Neothyonidium type.
