What is "tonguefish"

Tonguefish \Tongue"fish`\, n. (Zo["o]l.) A flounder ( Symphurus plagiusa) native of the southern coast of the United States.

n. Any of the flatfishes in the taxonomic family Cynoglossidae, distinguished by the presence of a long hook on the snout overhanging the mouth.

n. left-eyed marine flatfish whose tail tapers to a point; of little commercial value [syn: tongue-fish]

Tonguefishes are flatfishes in the family Cynoglossidae. 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. This family has three genera with a total of more than 140 species. The largest reaches a length of , though most species only reach half that size or less. They are found in tropical and subtropical oceans, mainly in shallow waters and estuaries, though a few species found in deep sea floors, and a few in rivers.

Symphurus thermophilus lives congregating around "ponds" of sulphur at hydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents. Scientists are unsure of the mechanism that allows the fish to survive and even thrive in such a hostile environment.