A zoological jewel in sight: two researchers report on the unusual discovery of a new and at the same time well-known species. They have found living specimens of a transparent, shimmering clam previously known only from Pleistocene fossil deposits in tide pools off the coast of California.
There is still much that is new to discover in the fascinating diversity of nature: zoologists are constantly expanding our knowledge of the biodiversity of our world. But the current case is something special, as reported by Jeff Goddard of the University of California at Santa Barbara and Paul Valentich-Scott of the Santa Barbara Museum of Natural History. The story goes back to a scientific survey at Naples Point on the southern Californian coast in November 2018: Actually, Goddard was there in the tide pools at low tide in search of special species of snails when he came across two strange shells while turning a stone: "Yours Shells were only ten millimeters long and then they started waving with a bright white striped foot that was longer than their shell. In my many inspections over the past few decades, I had never seen this species," says the marine biologist.
What is that strange shell?
Goddard decided not to take the apparently rare animals with him, but only to photograph them. He determined that they are members of the mussel family Galeommatidae, but could not identify the species. He then sent the images to expert Valentich-Scott. “I was surprised and intrigued. I know this family of mussels on the American coast very well. But I had never seen these representatives before,” reports the scientist. So there was the exciting possibility that it was a new species. In order to be able to make an accurate assessment, however, an investigation was necessary. So Goddard returned to Naples Point to look for more specimens of the mysterious shells. However, he was unsuccessful for a long time. Success only came when he was no longer expecting a find: he discovered a specimen that he and Valentich-Scott were able to use to identify the species.
"That's when the hunt began," says Valentich-Scott. To check whether it is a previously unknown species, the researchers combed through the scientific literature from 1758 to the present day. The features of the conch shell did not seem to match any known living form. But then the pair stumbled across clues in a 1937 report of fossil finds from a Pleistocene deposit six miles offshore in the Los Angeles area. They discovered striking similarities to images of a mussel, which at the time was given the species name Bornia cooki. Fortunately, a fossil specimen was stored at the Natural History Museum of Los Angeles County, which Valentich-Scott requested. This allowed the researchers to compare it with the newly covered one.
A living fossil
It was finally confirmed that the find was something like a living fossil: a species that was thought to be extinct. "It's not often that you find alive a species previously known only from fossils," says Goddard. "Our find does not go back nearly as far in the evolutionary history as in the case of the famous coelacanth, which was thought to have disappeared many millions of years ago. But it goes back to all those wondrous animals that were found in the famous La Brea tar pits in California. The animal fossils preserved in these asphalt pits date from the last Ice Age.
As Goddard and Valentich-Scott point out, the question now is how the shell could have remained undiscovered for so long. "There's a long tradition of shelling and studying mollusks in Southern California, so it's amazing that nobody has found even our sweetheart's shells," says Goddard. According to him, the actual home range of this species could be further south along the Mexican coast. In concrete terms, it could be that the mussels traveled north with the current as planktonic larvae during the heat waves of 2014 to 2016. As is well known, other sea creatures were also able to expand their distribution area to the north as a result. This species of mussel, which has now been identified as a living fossil, may also be one of them.
Source: University of California – Santa Barbara, professional article: Zookeys, doi: 10.3897/zookeys.1128.95139