This paper deals with the faunistic study of the sponges Demospongia of the catalan littoral. A extent of 250Km2, between Calella and Tossa, has been explorad by two methods: SCUBA-diving for depths ranging from 7 to 25 metres and trawling nets of fishing boats from 25m to 500m. Descriptions and illustrations of 19 species based on living specimens have.been made. Majar emphasis has been given to the skeletal patterns. Spicules and skeletal organitation has been drawn. Morphological and skeletal patterns of catalan specimens are confronted with those of specimens from different latitudes, depths and substrats described by others authors. Specimens of Aaptos aaptos, Stelligera rigida~ Raspaciona aculeata, Hemimycale columella and Suberites carnosus various growing shapes according to the changes of depth. In general, these species have a encrusting shape at the superficial levels, a masive shape at the intermediate levels, and they stand with a lobate or branchy shape at the deep levels. Water movements and presence'of sediment seem to be the cause of these growing variations. Some of the studied species have an special interest: Polymastia mammillaris and Pseudosuberites hyalinus are cited for the first time in the Spanish Mediterranean Sea; Stelligera rigida and Halichondria agglomerans are new records on the Iberian coasts and in the Mediterranean Sea, respectively. At last Spongosorites maxima es a new species. The second part of this study deals with sorne ecological aspects: relations between sponges and others benthonics invertebrates and sponges ditribution in the sampled area.