When is an aster not an aster? A new deep-sea Discorhabdella (Demospongiae, Poecilosclerida) with asters, from the Mozambique Channel

摘要

Discorhabdella pseudaster n. sp. is an incrusting sponge from the upper bathyal zone of the 'Banc du Geyser', north of Madagascar, Mozambique Channel This new species is described only from a single specimen but it is remarkable by the presence of spicules similar to euasters, a type of microsclere unknown in Poecilosclerida. These spicules are in fact a new example of homoplasy, being derivatives of the typical Discorhabdella pseudoastrose acanthostyles, which are here reduced to the aster-like tyles. The isochelae with a large lamella on the shaft are also quite unique in Poeciloclerida.