An eel recently discovered in an underwater cave appears to have evolved out of step with the rest of us, retaining primitive characteristics associated with animals from the dinosaur era.
The eel, described in the latest Proceedings of the Royal Society B, is what Charles Darwin referred to as a "living fossil." These are extremely long-lasting species that have undergone few bodily changes over the millennia.
In this case, the enigmatic eel dubbed Protoanguilla ("first eel") palau represents a new family, genus and species that dates back to around 200 million years ago.
"The eel looks so bizarre — large head with relatively short body and various unique, internal characters — that no ichthyologist, including us, correctly identified it as a member of true eel at first sight," co-author Masaki Miya told Discovery News. Miya is curator of fishes and an adjunct associate professor at Chiba University's Natural History Museum and Institute.
His colleague, diver Jiro Sakaue, found the eel nearly 115 feet under the surface of the Pacific Ocean in a cave at the western fringing reef of Ngemelis Island in the Republic of Palau. Although just 1.7 inches long, the eel's reddish brown body is striking, especially given its iridescent fins tipped in bright white.
Both morphological and molecular analysis place Protoanguilla in a sister lineage independent of other eels. There are more than 800 species of true eels, classified into 19 families. The oldest-known eel in the fossil record dates to 100 million years ago, and this newly discovered species remarkably has features even more ancient than that.
"Those characters assumed to be more primitive than, and equally primitive with, the oldest fossil record actually represent those descended from the dinosaur era," Miya said.
Lead author David Johnson explained that these primitive features include fewer vertebrae, certain fused skull bones, presence of an upper jaw bone found in Cretaceous eels, and toothed gill rakers, which could be involved in feeding and gill maintenance.
Johnson, curator of the Division of Fishes at the Smithsonian National Museum of Natural History, added that the eel's "tail fin rays extend back slightly farther than the adjacent fin rays. This is another feature in which Protoanguilla appears to be primitive with respect to living eels."
Co-author Hitoshi Ida shared that the cave home of this eel "is extremely young (110,000 to 10,000 years ago) compared with the evolutionary history of the living fossil eel."
"I think that what we see is a remnant of their habitat," Ida said.
It's possible that this unusual eel may be found in other remote marine habitats, but so far, the small Palau cave is its only known home.
John McCosker, chair of aquatic biology at the California Academy of Sciences, told Discovery News that he and other eel experts are "chagrined that such a remarkable eel turned up in an underwater cave in Palau."
"Eels, to most amateur naturalists, aren't even thought of as fish," McCosker said. "They are, in fact, an excellent case of evolution involving the loss of body parts rather than their exaggeration, and in discovering the basal lineage of true eels, the authors have helped to trace the process of eel evolution further back in its ancestry."
He added, "The analysis they have performed using morphology and genetics is brilliant and invites as many questions about eel evolution as it solves."
One particularly important question that remains about this eel, like all newfound species, is what now can be done to protect it. The researchers expressed concern, given that its uniqueness and location are now known.
"Professional as well as amateur divers are always curious about animals and those working for the aquarium trade are notorious for trying to keep every animal in their tanks," Miya said. "We should promote a campaign for preserving animals to the Palau government shortly after the (study's) publication."