TAXONOMIC REVISION OF THE MEDITERRANEAN PLAKINA SCHULZE (PORIFERA, DEMOSPONGIAE, HOMOSCLEROMORPHA)

Only three species of the sponge genus Plakina Schulze have been descr ibed from the Mediterranean since 1880, in spite of a large amount of allegedly intraspecific variability in morphological characters. Howev er, recent genetic studies based on electrophoretic techniques have re vealed extensive cryptic speciation in north-western Mediterranean Pla kina, demonstrating that most of this variation was interspecific rath er than intraspecific. We describe in detail the morphology and anatom y of four new species of Plakina from the Mediterranean-P. crypta, P. weinbergi, P: endoumensis and P. jani-of which the latter two were dis covered through allozyme electrophoresis. Plakina monolopha Schulze an d P. trilopha Schulze are redescribed, and their morphological and geo graphical limits are discussed along with those of P. dilopha Schulze. Accurate analysis of the internal anatomy and of the shape and ramifi cation pattern of lophose spicules in scanning electron microscopy pro vides new, powerful morphological criteria for species discrimination in Plakina. More widespread use of such new taxonomic characters shoul d provide evidence against the alleged cosmopolitanism of some Plakina species, thus generating an increase in estimates of the biodiversity of plakinids. (C) 1998 The Linnean Society of London.