The Mediterranean Sea is a remnant of the Tethys Ocean, a wedge-shaped, eastward-open equatorial sea that indented Pangea during the Triassic (Fig. 7.1) (Dutch 1998). The Tethys Sea connected, through an uninterrupted equatorial belt, the newly born ocean to the older Indo-Pacifi c Ocean after the opening of the Atlantic Ocean during the Cretaceous. During that time, the Tethys Sea harboured a highly diverse warm-water fauna from the tropical Indo-West Pacifi c Ocean (Dutch 1998, Bianchi and Morri 2000). In the Miocene orogeny, plate collisions sealed off the eastern Mediterranean Sea, trapping small remnants of ocean fl oor in the Black and Caspian Seas. At that time, the Isthmus of Suez was formed, separating the Mediterranean Sea from the Indo-Pacifi c Ocean. The connection between the Mediterranean Sea and the Atlantic Ocean was also closed at the end of the Miocene, and the Mediterranean Sea became a closed and isolated sea. River infl ow was not enough to maintain the level of the Mediterranean, which dried out. Dehydration of the closed Mediterranean Sea might have driven the Tethyan deep water fauna to extinction (Bouchet and Taviani 1992), but at least part of the shallow-water biota may have survived through the Neogene (Stanley 1990, Bellan-Santini et al. 1992, Myers 1996, Bianchi and Morri 2000). After the re-opening of the Straits of Gibraltar at the dawn of the Pliocene (6 million years ago), the Mediterranean Sea was re-populated by species of Atlantic origin and the Mediterranean Sea biota became that of an Atlantic province (Briggs 1974, Briggs and Bowen 2012, Bianchi and Morri 2000, Spalding et al. 2007). The word Mediterranean derives from the Latin mediterraneus, meaning ‘in the middle of earth’ or ‘between lands’ (medius, ‘middle, between’ + terra, ‘land, earth’). This is on account of the sea’s intermediary position between the continents of Africa and Europe.