Synaphobranchus calvus is an eel in the family Synaphobranchidae (cutthroat eels). It was described by Marcelo Roberto Souto de Melo in 2007. It is a marine, tropical eel which is known from Brazil, in the southern Atlantic Ocean. It dwells at a depth range of 750 to 2,000 metres (2,460 to 6,560 ft). Males can reach a maximum total length of 68.5 centimetres (27.0 in). The species epithet "calvus" means "bald" in Latin, and refers to the lack of scales on the eel's head.