A new species of Asterodiscides (Echinodermata, Asteroidea, Asterodiscididae) from the tropical southwest Pacific, and the biogeography of the genus revisited

A new species of Asterodiscides, A. bicornutus n. sp., is reported from Espiritu Santo, Vanuatu, in the tropical southwest Pacific, a region which may qualify as a southeastern extension of the zone of maximum marine biodiversity known as the coral triangle. The biogeography of the genus, in particular its apparent absence from the equatorial Indo-Malay and west Pacific region and the occurrence of disjunct distributions, is re-examined. An earlier contention that this anomalous distribution pattern could result from shelf extinctions during glacial maxima, with subsequent failure to re-invade the core diversity region during high sea level stands, is rejected. Tropical Asterodiscides species generally occur at depths corresponding to the ocean thermocline, an undersampled zone that is deeper in the west Pacific. Further intensive surveys for these comparatively rare asteroids in the core biodiversity region, sampling deeper shelf areas and targeting upwelling zones, together with supportive molecular analyses and investigation of biology (particularly reproductive strategies), are considered essential for a more complete understanding of the biogeography and speciation of this genus.