They are distinguished by the presence of a long hook on the snout overhanging the mouth, and the absence of pectoral fins.

Their eyes are both on the left side of their bodies, which also lack a pelvic fin.

[3][4][5] They are found in tropical and subtropical oceans, mainly in shallow waters and estuaries, though some species are found in deep sea floors,[6] and even a few in rivers.

Symphurus thermophilus lives congregating around "ponds" of sulphur at hydrothermal vents on the seafloor.

[7] Scientists are unsure of the mechanism that allows the fish to survive and even thrive in such a hostile environment.