Tonguefishes are flatfish 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.[2] This family has three genera with a total of more than 140 species. The largest reaches a length of 66 cm (26 in), though most species only reach half that size or less.[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.
| Tonguefishes | |
|---|---|
| |
| Northern tonguefish, Symphurus pusillus | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Pleuronectiformes |
| Family: | Cynoglossidae Jordan, 1888 |
| Subfamilies & Genera[1] | |
|
Subfamily Cynoglossinae Subfamily Symphurinae | |
Symphurus thermophilus lives congregating around "ponds" of sulphurathydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents.[7] Scientists are unsure of the mechanism that allows the fish to survive and even thrive in such a hostile environment.[8]