Symphurus thermophilus

Symphurus thermophilus is a species of tonguefish notable for being the only flatfish known to be an obligate inhabitant of hydrothermal vents. It is known from several widely dispersed locations in the western Pacific Ocean and occurs in great numbers. They are tolerant of harsh conditions and are often found in close association with elemental sulfur, including molten sulfur pools that exceed 180 °C in temperature. As they are not significantly different in appearance and feeding habits from other tonguefishes, they are thought to be relatively recent colonizers of vent ecosystems.

These fish were first observed in nature in 1988, and were provisionally assigned to the species Symphurus orientalis before being recognized as a new species. The species name thermophilus is from the Greek thermos meaning "heat" and philos meaning "lover", referring to its association with hydrothermal vents.