The sponge genus Brachiaster (Pachastrellidae, Demospongiae) and its first known fossil representative, from the late Eocene of southwestern Australia

Abstract

Pisera, A. & Bitner, M.A., December, 2007. The sponge genus Brachiaster (Pachastrellidae, Demospongiae) and its first known fossil representative, from the late Eocene of southwestern Australia. Alcheringa 31, 365‐373. ISSN 0311-5518. The pachastrellid genus Brachiaster Wilson (Pachastrellidae, Demospongiae, Porifera) has had until now no known fossil representatives. Here we describe its first known fossil representative from the late Eocene of southwestern Western Australia, assigned to Brachiaster claudelevii sp. nov. Brachiaster claudelevii has well-developed axial canals in the mesotriders, which points to it being intermediate in character between the typical tetraxial desmas of lithistids, and tetraxial spicules of non-lithistid demosponges. This further supports the position of Brachiaster among the Pachastrellidae. The geographic and bathymetric distribution of the extant and newly described fossil representatives of Brachiaster indicates that the Eocene sponge described here is important in understanding the evolution of Indo-West Pacific sponges because it points to a long evolutionary history and complex biogeographic distribution of this lineage of pachastrellid sponges. Andrzej Pisera [apis@twarda.pan.pl], Maria Aleksandra Bitner [bitner@twarda.pan.pl], Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/55, 00‐818 Warszawa, Poland; received 24.3.2006; revised 14.6.2006.