A species of clam thought to exist only as a fossil has been found living off the coast of California.
But a living identical clam was found by Doctor Jeff Goddard while turning over rocks in search of a species of sea slug called nudibranch.
Dr Goddard, of University of California, Santa Barbara, said: “It's not all that common to find alive a species first known from the fossil record, especially in a region as well-studied as Southern California.
“Ours doesn't go back anywhere near as far as the famous Coelacanth or the deep-water mollusc Neopilina galatheae – representing an entire class of animals thought to have disappeared 400 million years ago – but it does go back to the time of all those wondrous animals captured by the La Brea Tar Pits.”
Dr Goddard told how one afternoon in November 2018 while trawling the beach at Naples Point he saw a pair of small translucent bivalves – molluscs that live within enclosed shells.
He said: “Their shells were only 10 millimetres long, but when they extended and started waving about a bright, white-striped foot longer than their shell, I realised I had never seen this species before.”
Surprised and believing it to be rare, he left the clam undisturbed but took close-up photos of the animals which he then sent on to Paul Valentich-Scott, curator emeritus of malacology at the Santa Barbara Museum of Natural History.
He said: “I was surprised and intrigued. I know this family of bivalves very well along the coast of the Americas. This was something I’d never seen before.”
The curator said he would need to see the animal in-person to assess it properly so Dr Goddard returned to Naples point but failed to find the clam after two hours of searching.
It took a further nine trips for him to make his rediscovery, in March 2019.
Mr Valentich-Scott said he was even more surprised once he got his hands on the shell.
He knew it belonged to a genus with one member in the Santa Barbara region, but this shell didn’t match any of them, suggesting the possibility of a new species.
He said: “This really started the hunt for me. When I suspect something is a new species, I need to track back through all of the scientific literature from 1758 to the present. It can be a daunting task, but with experience it can go pretty quickly.”
That is when the two researchers stumbled upon George Willett’s 1937 description, which he had named Bornia cooki after Edna Cook, a fellow collector in the region who had found the only two specimens known to exist.
Mr Valentich-Scott requested the original specimen, now called Cymatioa cooki, from the Natural History Museum of Los Angeles County, which he used as a type specimen – the example that defines the species.
In the meantime, Dr Goddard had found another live example at Naples Point, a single empty shell in the sand underneath a boulder.
Through careful comparison of the living specimens and the fossil, Mr Valentich-Scott concluded that they were the same species, describing the find as “pretty remarkable”.
Wondering how the clam eluded detection for so long, Dr Goddard said: “There is such a long history of shell-collecting and malacology in Southern California –including folks interested in the harder to find micro-molluscs – that it's hard to believe no one found even the shells of our little cutie.”
He believes it may have arrived on currents as planktonic larvae, carried up from the south during marine heatwaves from 2014 through 2016.
These allowed many marine species to extend themselves northward, including several documented specifically at Naples Point.
Depending on the animal’s growth rate and longevity, this could explain why no one had noticed Cymatioa cooki prior to 2018, including Dr Goddard, who has worked on nudibranchs at Naples Point since 2002.
He said: “The Pacific coast of Baja California has broad intertidal boulder fields that stretch literally for miles and I suspect that down there Cymatioa cooki is probably living in close association with animals burrowing beneath those boulders.”
The findings were published in the journal Zookeys.