ORIGIN AND BIOGEOGRAPHY OF THE DEEP-WATER MEDITERRANEAN HYDROMEDUSAE INCLUDING THE DESCRIPTION OF 2 NEW SPECIES COLLECTED IN SUBMARINE CANYONS OF NORTHWESTERN MEDITERRANEAN

Two new species of hydromedusae (Foersteria antoniae and Cunina simple x) are described from plankton collected in sediment traps placed in t he Lacaze-Duthiers Submarine Canyon and along Banyuls-sur-Mer coast (n orthwestern Mediterranean). The Mediterranean hydromedusan deep-water fauna contains 41 species which represent 45.5 % of the world-wide dee p-sea hydromedusae fauna (90) and 20% of the total number of Mediterra nean hydromedusae (204). The Mediterranean deep-water hydromedusan fau na is characterised by a large percentage of holoplanktonic species (6 1%), mainly Trachymedusae. Nevertheless, contrary to the general opini on, the percentage of meroplanktonic species is equally high. The most original features of this fauna lies however in the importance of the number of endemic species (22%) and in the fact that the majority of them are meroplanktonic Leptomedusae with a supposed bathybenthic stag e. Some of the endemic species could still represent relies of the pri mitive Tethys fauna having survived to the Messinian crisis. The origi n of the Mediterranean deep-water hydromedusan fauna is discussed and a general hypothesis is proposed.