‘Lithistid’ Demospongiae

Abstract

‘Lithistid’ demosponges are a polyphyletic group (formerly order Lithistida Schmidt, 1870) containing 13 extant families and 36 included genera, plus five poorly known genera of uncertain status (most probably synonyms of other genera but their affinities are not yet certain). The only shared character amongst the lithistids is the presence of more-or-less irregular articulated choanosomal spicules called desmas, which form a rigid skeleton in most genera. The polyphyletic nature of ‘lithistids’ is revealed by the wide array of geometry (tetraxial, monaxial, polyaxial or anaxial) of its desmas and of ectosomal spicules (dichotriaenes, phyllotriaenes, discotriaenes, rhabds, oxeas, or pseudodiscotriaenes and pseudophyllotriaenes), as well as microscleres (amphiasters, spirasters, sigmaspires, raphides). We propose here, for the reason of their undoubted polyphyletic nature, to formally abandon the order Lithistida Schmidt, both for Recent and fossil lithistids.