GENETIC-EVIDENCE FOR EXTENSIVE CRYPTIC SPECIATION IN THE SUBTIDAL SPONGE PLAKINA-TRILOPHA (PORIFERA, DEMOSPONGIAE, HOMOSCLEROMORPHA) FROM THE WESTERN MEDITERRANEAN

To date, only 3 species of the sponge genus Plakina Schulze have been identified in the Mediterranean: P, monolopha, P, dilopha and P. trilo pha. These species are distinguished on the basis of the presence of a particular spicule type (lophocalthrops) with 1, 2 and 3 lophate acti nes, respectively. In a survey of plakinids on vertical walls and subm arine caves in the Mediterranean around Marseilles, France, we found 4 different morphotypes of what would normally be identified as P. tril opha (i.e. with trilophose calthrops). However, slight but consistent differences in morphological characters and ecology led us to doubt th e conspecificity of these morphotypes. Genetic divergence and reproduc tive isolation between morphotypes were investigated through allozyme electrophoresis. It was found that all 4 morphotypes were reproductive ly isolated from each other, with diagnostic loci between any pair of morphotypes compared. Genetic identities between morphotypes ranged fr om 0.49 to 0.83. The genetic differences found between the morphotypes indicate that these should not be considered conspecific. Once specie s boundaries were delimited by genetic data, diagnostic morphological characters for each species could be found.