A geographical study of the littoral sponges from the Straits of Gibraltar was undertaken, where the origin of these sponges is observed to be a transition between the different geographic regions that meet in the Straits. A great affinity was also observed between the Mauretanian fauna, the fauna from the Straits of Gibraltar and that from the entire Spanish Peninsular Mediterranean, thus conforming a very homogeneous block within the group of areas studied. On the other hand, a numerous group of species traditionally considered endemic to the Mediterranean, such as: Haliclona mucosa, H. valliculata, H. cratera, H. fulva, H. aqueductus. H. mediterranea, Dendroxea lenis, Phorbas tenacior, Hexadella racovitzai, Ircinia oros, Dictyonella incisa, Acanthella acuta, Diplastrella bistellata, etc. are believed to have an origin in tropical or subtropical Alantic waters.