has a long history of different taxonomic assignments.
In the past they have been placed in seven different
catfish families, in the "Parasitic Catfishes"
(Trichomycteridae), the "Walking catfishes"
(Clariidae) the Whale Catfishes (Cetopsidae),
the eel and coral catfish (Plotosidae) the Olyridae,
the "Pim cats" (Pimelodidae) and the
Heptapteridae , to which Phreatobius
belongs as a sister genus of Gladioglanis
in most of today's classifications.
comparisons show, however, that Phreatobius
has been developing independently for a very
long time and is the sister genus of a clade
from the Pimelodidae
and the Pseudopimelodidae. At the momemt (2021)
there are three described species in this genera,
P. cisternarum Goeldi, 1905,
P. dracunculus Shibatta, Muriel-Cunha
& De Pinna, 2007, and P. sanguijuela
Fernández, Saucedo, Carvajal-Vallejos
& Schaefer, 2007.