The 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.
The body is very small and slender, about 18 cm long. They have a second premaxilla and under 90 vertebrae, features previously found only in fossilised eels. Their full set of gill rakers in their branchial arches have never previously been found in an eel, but are common in bony fish. It is so different from all other living eels, 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 its own genus and family, as well, and has been referred to by scientists as a "living fossil".