Rare fossil clam discovered alive

Discovering a new species is always exciting, but so is finding a living one that everyone assumed had been lost over time. A small clam, previously known only from fossils, was recently found living at Naples Point, just up the coast from UC Santa Barbara. The discovery appears in the newspaper Zookeys.

“It’s not that common to find a known species alive for the first time in the fossil record, especially in an area as well-studied as southern California,” said co-author Jeff Goddard, associate researcher at the Marine Science Institute at UC Santa Barbara. “Ours does not date back as far as the famous Coelacanth or the deep-sea mollusc Neopilina galatheae – representing a whole class of animals thought to have died out 400 million years ago – but it dates back of all those wonderful animals captured by the La Brea tar pits.”

On an afternoon at low tide in November 2018, Goddard was digging up rocks in search of nudibranch sea slugs at Naples Point, when a pair of small, translucent bivalves caught his eye. “Their shells were only 10 millimeters long,” he said. “But when they stretched out and started wiggling a bright white striped foot longer than their shell, I realized I had never seen this species before.” This came as a surprise to Goddard, who has spent decades in California’s intertidal habitats, including many years specifically at Naples Point. He immediately stopped whatever he was doing to take close-up photos of the intriguing animals.

With quality images in hand, Goddard decided not to collect the animals, which seemed rare. After identifying their taxonomic family, he sent the images to Paul Valentich-Scott, curator emeritus of malacology at the Santa Barbara Museum of Natural History. “I was surprised and intrigued,” recalls Valentich-Scott. “I know this family of bivalves (Galeommatidae) very well along the coast of the Americas. It was something I had never seen before.”

He mentioned a few possibilities to Goddard, but said he would need to see the animal in person to make a proper assessment. So, Goddard returned to Naples Point to claim his clam. But after two hours of combing through a few square meters, he still hasn’t seen his price. The species would continue to elude him many times.

Nine trips later, in March 2019, and almost ready to give up for good, Goddard turned over yet another rock and saw the needle in the haystack: a single specimen, alongside a few small white nudibranchs and a big kitten. Valentich-Scott would finally get his specimen, and the pair could finally get to work on identification.

Valentich-Scott was even more surprised once he got his hands on the hull. He knew he belonged to a gender with a member in the Santa Barbara area, but that shell didn’t match any of them. This raised the exciting possibility that they had found a new species.

“It really started ‘the hunt’ for me,” Valentich-Scott said. “When I suspect it’s a new species, I have to sift through all the scientific literature from 1758 to the present day. It can be a daunting task, but with experience it can go quite quickly.”

The two researchers decided to verify an intriguing reference to a fossil species. They found illustrations of the bivalve Bornia cooki from the article describing the species in 1937. It seemed to match the modern specimen. If this were confirmed, it would mean that Goddard did not find a new species, but some kind of living fossil.

It should be noted that the scientist who described the species, George Willett, estimated that he had excavated and examined perhaps 1 million fossil specimens from the same location, the Baldwin Hills in Los Angeles. That said, he never found B. cooki himself. Instead, he named it after Edna Cook, a Baldwin Hills collector who had found the only two known specimens.

Valentich-Scott requested the original Willett specimen (now classified as a Cymatioa cookie) from the Natural History Museum of Los Angeles County. This object, called a “type specimen”, serves to define the species, so it is the ultimate arbiter of the clam’s identification.

Meanwhile, Goddard found another specimen at Naples Point – a single empty shell in the sand under a rock. After carefully comparing the Naples Point specimens with the Willett fossil, Valentich-Scott concluded that they were the same species. “It was quite remarkable,” he recalls.

Despite its small size and cryptic habitat, it all begs the question of how the clam evaded detection for so long. “There’s such a long history of shell collecting and malacology in Southern California — including people interested in the hardest-to-find micro-molluscs — that it’s hard to believe no one has even found our little cutie’s shells,” Goddard said.

He suspects that the clams may have arrived here on the currents as planktonic larvae, transported from the south during the marine heat waves of 2014 to 2016. These allowed many marine species to expand their distribution to the north, including several documented specifically at Naples Point. Depending on the animal’s growth rate and longevity, this could explain why no one noticed C. cooki at the site until 2018, including Goddard, who has worked on nudibranchs at Naples Point since 2002.

“The Pacific coast of Baja California has vast intertidal rock fields that literally stretch for miles,” Goddard said, “and I suspect that there Cymatioa cooki probably lives in close association with burrowing animals. under these rocks.