Dredgings and in situ observations (from the submersibleCYANA) undertaken in different areas of the Mediterranean Sea show that communities, chiefly composed of sponges and/or scleractinians and serpulids have colonized rocky bottoms, of subsea bathyal relief features, i.e. as far as 2500–3000 m. These faunas, not very diversified are now fossilized. There are some regional and local variations in thedensity of populations but, in several sites, particularly in the Tyrrhenian Sea and along the Malta escarpment, concentration in individuals can be high. In this case, their skeletons constitute the frame of decimetric to metric edifices of constructed limestones. The paleocommunities are contemporaneous withthe last cold climatic phase of the Pleistocene. Their development might have been favoured by the presence of deep-currents. The latters initiated superficial and early cementations which have affected associated micritic material during periods of absence of sedimentation. The disappearance of these Mediterranean assemblages is probably related to several concomitant factors; in particular to an increase in temperature of deep-waters and to a decrease in food supply.