Scientists from the Smithsonian and partnering organizations have discovered a new eel that inhabits an undersea cave in the Pacific Ocean which they have dubbed a "living fossil".The U.S.-Palauan-Japanese team had to create a new taxonomic family to describe its relationship to other eels.
The team say the eel's features suggest it has a long and independent evolutionary history stretching back 200 million years.
The animal is brown and has very few of the anatomical characteristics of modern eels. It features a disproportionately large head, a short compressed body, collar-like openings on the gills, rays on the caudal fin and a jawbone tip known as the premaxilla.
The animal used as the basis for the new study was a 7-inch long female, collected by one of the researchers during a dive at a 114-feet-deep cave in the Republic of Palau.
The scientists collected the eels using nets and lamps to collect DNA for tests.
Genetic analysis of the eel species confirmed that the fish was a "true" eel, but a primitive one.
"In some features it is more primitive than recent eels, and in others, even more primitive than the oldest known fossil eels, suggesting that it represents a 'living fossil' without a known fossil record," the scientists wrote in the journal Proceedings of the Royal Society B.
The researchers had to create a new family, genus and species in order to classify the new animal.
The team drew up a family tree of different eels, showing the relationships between them.
This allowed them to estimate when the ancestors of P. palau split away from other types of eel.
The team's results suggest this new family has been evolving independently for the last 200 million years, placing their origins in the early Mesozoic era.
The researchers say that the eel must have once been more widely distributed because the undersea ridge where its cave home is between 60 and 70 million years old.
Image Caption: Scientists at the Smithsonian and partnering organizations have discovered a remarkably primitive eel 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. Credit: Jiro Sakaue