Pyrococcus sp. strain ST04 was isolated in May 2004 from a piece of a hydrothermal sulfide chimney that was emitting hydrothermal fluid at temperatures up to 302°C and a depth of 2,290 m. The sample was collected from the Stonehenge mound in the Mothra vent field along the Endeavour Segment of the Juan de Fuca Ridge using the deep-sea research submarine Alvin.