An impossible habitat
More than 3,000 meters below the surface of the Mediterranean Sea lies the L'Atalante basin, a depression on the seafloor filled with a brine so dense it does not mix with the water above it. This brine has a salinity of 365 g/L, about eight times saltier than normal seawater, and is completely anoxic—it contains no oxygen. The basin formed when ancient salt deposits dissolved, creating a permanently stratified, oxygen-free lake on the ocean floor. This extreme environment, containing toxic sulfides, was long considered inhospitable to any form of animal life.
In 2010, a research team led by Roberto Danovaro reported a discovery from the basin's dark, sulfidic sediments: three species of multicellular animals, or metazoans, that live their entire lives without oxygen. These animals belong to the phylum Loricifera, a group of microscopic invertebrates also known as "corset animals" for their protective outer shell, or lorica. The three species found in the L'Atalante basin were Spinoloricus cinziae, Rugiloricus nov. sp., and Pliciloricus nov. sp. Prior to this, scientists believed that multicellular animals could only tolerate anoxic conditions temporarily. The discovery of loriciferans completing their full life cycle—evidenced by the presence of adults, larvae, and shed exoskeletons—in a permanently anoxic place was unprecedented.