Protanguilla palau is a species of eel, the only species in the genus Protanguilla (first eel), which is in turn the only genus in its family, Protanguillidae.

Individuals were found swimming in March 2010 in a deep underwater cave in a fringing reef off the coast of Palau.

Its full set of gill rakers in its branchial arches has never previously been found in an eel, but is common in bony fish.

[7] It is very different from all other living eels, and scientists estimate it must have diverged from the others around 200 million years ago, during the Mesozoic era.

It thus has not only its own species, but also its own genus and family, as well, and has been referred to by scientists as a "living fossil".