Evolutionary origins of hydrothermal vents metazoans

Abstract. The discovery of the oases associated with hydrothermal vents in the deep sea, is probably the most fascinating discovery of oceanography of the last century. In this habitat, contrary to all expectations, a thriving development of unknown organisms was observed. At that time the knowledge about the deep sea organisms was very scarce and the accepted hypotheses about their evolutionary origins, their physiology or their ecology were very speculative. Almost forty years later, exploration of the deep-sea realm, but also of paleontological data together with the improvements in the phylogenetic methods, allowed the rejection of the hypothesis of an evolutionary history cut off the rest of the marine realm. 1. Life in the deep sea: Knowledge is recent In the thirty years after the discovery of the deep-sea oases associated with hot vents much of the research efforts of the marine biologists have been devoted to this exceptional environment and its inhabitants. However, when the hot vents have been discovered, the deep-sea realm was still poorly known. At this time, most of the available hypotheses about the functioning of deep sea ecosystems, or about the physiology or the evolutionary origins of the organisms were very speculative. In this historical context, I selected three hypotheses which I feel have played a major role in the analysis of the diversity of ho