Scientists have described a new type of eel, which is found living in an undersea cave in the Pacific Ocean, as the living fossil due to its primitive features.

The species is so unique that the scientists had to create a new taxonomic family to describe its relationship to other eels. The team of scientists from the US, Japan and Palaua believe that the eel has an evolutionary history that dates back to 200 million years.

The specimen for the study was collected by a researcher during a dive at a 35m-deep cave in the Republic of Palau. The scientists carried out genetic analysis to confirm that the fish is indeel an eel but with primitive features.

"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," write the scientists.

The team - including Masaki Miya from Chiba's Natural History Museum in Japan, Jiro Sakaue from the Southern Marine Laboratory in Palau and G David Johnson from the Smithsonian Institute in Washington DC developed a fmaility ttree showing relationship between the eels. The research paper also includes references to other species of ells

The study has been published in the in the journal Proceedings of the Royal Society B.