Gnathophis mystax, the thinlip conger or blacktailed conger, is an eel in the family Congridae (conger/garden eels). It was described by François Étienne Delaroche in 1809, originally under the genus Muraena.

Gnathophis mystax, the thinlip conger or blacktailed conger, is an eel in the family Congridae (conger/garden eels). It was described by François Étienne Delaroche in 1809, originally under the genus Muraena. It is a subtropical, marine eel which is known from the eastern Atlantic Ocean, including southern Portugal, the Mediterranean, and Morocco.