Systema Proifera: a guide to the classification of sponges....The end of a beginning

The Systema Porifera collaboration (45 authors from 17 countries) produced a two volume treatise revising and defining the supraspecific classification of sponges and spongiomorphs (Kluwer Academic / Plenum Publishers). The Systema recognises approximately 680 genera of living sponges and 1000 genera of fossil sponges from many thousands of nominal taxa, and places these taxa in a unified higher systematics scheme (including over forty new higher taxa proposed). Most genera were revised from their type material (where available), reinterpretation of the vast sponge literature, and incorporation of other biological evidence where available. The Systema, therefore, has an important theoretical basis, being: the most comprehensive taxonomic revision of sponges at genus level and above; addressing the many long-outstanding nomenclatural problems (and thus stabilising the nomenclature) and providing a sound baseline to focus detailed research questions on sponges in the future. It also has a strong practical focus as a tool for sponge identification: providing concise definitions, diagnoses, keys and illustrations of all the valid (i.e., reinterpreted) genera of extant sponges, and some key fossil sponge genera, unified into a single classification of Porifera; serving as a manual to achieve more accurate faunal inventories that will be of benefit to biodiversity and biogeographic analyses etc., and thus marine conservation and planning. In this paper we critically analyse the strengths (achievements) and weaknesses (remaining challenges) of the Systema Porifera project, and highlight some areas where research might be productively directed in the future, including questions of the monophyly of Porifera itself.