See text The viviparous brotulas form a family, the Bythitidae, of ophidiiform fishes.

They are known as viviparous brotulas as they generally bear live young,[1] although there are indications that some species (at least Didymothallus criniceps) do not.

[5] Thermichthys hollisi, which lives at depths of around 2,500 m (8,200 ft), is associated with thermal vents.

[6] A few are fresh or brackish water cavefish: the Mexican blind brotula (Typhliasina pearsei), Galapagos cuskeel (Ogilbia galapagosensis), Diancistrus typhlops and some Lucifuga species.

[10] In some classifications the family Aphyonidae is placed within the Bythitidae and the tribe Dinematichthyini of the subfamily Brosmophycinae has been raised to the status of a family, the Dinematichthyidae which contains 25 genera and 114 species.