Scientists at the Smithsonian and partnering organizations have discovered a remarkably primitive eel they have named Protoanguilla palau in a fringing reef off the coast of the Republic of Palau.

This fish exhibits many primitive anatomical features unknown in the other 19 families and more than 800 species of living eels, resulting in its classification as a new species belonging to a new genus and family. 

Many of the physical features of Protoanguilla palau reflect its relationship to the 19 families of Anguiliformes (true eels) currently living. Other, more primitive physical traits, such as a second upper jaw bone (premaxilla) and fewer than 90 vertebrae, have only been found in fossil forms from the Cretaceous period (140 million to 65 million years ago). 

one of 10 specimens the scientists used to describe Protoanguilla palau -- a species they are calling a living fossil. Credit: Jiro Sakaue

Still other traits, such as a full set of bony toothed "rakers," in the gill arches are a common feature in most bony fishes, but lacking in both fossil and living eels. The team's analyses of total mitochondrial DNA indicate that Protoanguilla palau represents an ancient, independent lineage with an evolutionary history comparable to that of the entire order of living and fossil eel species.

Citation: G. D. Johnson, H. Ida, J. Sakaue, T. Sado, T. Asahida, M. Miya. A 'living fossil' eel (Anguilliformes: Protoanguillidae, fam. nov.) from an undersea cave in Palau. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.1289