The deepest-living animal ever found lives 3.6km underground in scalding rock water

In 2011, researchers pulled a previously unknown nematode worm from water sampled 3.6 kilometres below the surface in a South African gold mine, where temperatures reach around 37°C and oxygen is scarce. Nicknamed the 'devil worm,' it shattered assumptions that multicellular animals couldn't survive at such crushing depths, previously thought to be the exclusive domain of single-celled microbes.

— Gaetan Borgonie et al., Nematoda from the terrestrial deep subsurface of South Africa — Nature, 2011