These ecosystems on the very deep seafloors (3000-6000m) of all oceans support a low biomass but high diversity of small invertebrates and microbes, along with larger crustaceans, demersal fish and echinoderms like starfish. Tracks and burrows of larger organisms in fine sediments that may be up to thousands of metres thick, structure habitat for smaller invertebrates. The absence of light, scarcity of food, and extreme hydrostatic pressures limit the density and biomass of organisms as well as the interactions among them. Inaccessible and little known, exploration of these ecosystems continue to reveal large numbers of species new to science.