An overview is proposed of the hexactinellid sponge fauna of the Mediterranean Sea, including the description of a new species of Sympagella, S. delauzei sp. nov., collected by ROV during the exploration of deep-sea canyons of the NW Mediterranean and of deep banks and seamounts of the Alboran Sea. The type species of Sympagella, S. nux, is redescribed from specimens from the type locality. An 18S rDNA sequence of the new species was obtained and included in a phylogenetic tree of related hexactinellids. Some modifications to the classification of Rossellidae are proposed according to the new morphological and molecular data obtained during this study: the genera Caulophacus, and Caulophacella are accordingly moved from Rossellinae to Lanuginellinae.