Ilyophis nigeli is an eel in the family Synaphobranchidae (cutthroat eels). It was described by Yuri Nikolaevich Shcherbachev and Kenneth J. Sulak in 1997. It is a marine, deep water-dwelling eel which is known from Japan, in the northwestern Pacific Ocean. It is known to dwell at a depth range of 700 to 1,800 metres (2,300 to 5,900 ft). Males can reach a maximum total length of 51.3 centimetres (20.2 in). The species epithet "nigeli" was given in honour of Nigel R. Merrett, credited with making "substantial contributions" to the knowledge of the synaphobranchid eels.