Rare fossil mussel discovered alive

Discovering a new species is always exciting, but so is finding a living creature that everyone assumed was lost over time. A small clam, previously known only from fossils, was recently found at Naples Point, just off the coast of UC Santa Barbara. The discovery appears in the magazine zookeys.

“It’s not that common to find a species alive that was first known from the… fossil recordespecially in a region as well-studied as Southern California,” said study co-author Jeff Goddard, a research associate at UC Santa Barbara’s Marine Science Institute. “Ours doesn’t go as far back as the famous Coelacanth or the deep — aquatic mollusk Neopilina galatheae – which represents a whole class of animals thought to have disappeared 400 million years ago – but it goes back to the time of all those wondrous animals that were caught by the La Brea Tar Pits.”

One afternoon in November 2018, Goddard was turning over rocks in search of 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 waving a bright white striped foot that was longer than their carapace, I realized I’d never seen this species before.” This surprised Goddard, who has spent decades in California’s tidal habitats, including many years specifically at Naples Point. He immediately stopped what 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 turned out to be rare. After locating their taxonomic family, he sent the images to Paul Valentich-Scott, malacology curator emeritus 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 America. This was something I had never seen before.”

He mentioned a few possibilities to Goddard, but said he had to see the animal in person to make a proper assessment. So Goddard returned to Naples Point to take his… mussel. But after two hours of combing just a few square feet, he still hadn’t seen his prize. The species would continue to avoid him many more times.

Nine trips later, in March 2019, and almost ready to give up for good, Goddard turned over another stone and saw the needle in the haystack: a single specimen, alongside a few small white slugs and a large chiton. Valentich-Scott would finally get his copy and the couple could finally get to work on identification.

Valentich-Scott was even more surprised when he got his hands on the bowl. He knew it belonged to a single-membered genus in the Santa Barbara area, but this shell didn’t match any of them. It raised the exciting possibility that they had found a new species.

“This really started ‘the hunt’ for me,” Valentich-Scott said. “If I suspect something is a new species, I have to search all the scientific literature from 1758 to the present day. It can be a daunting task, but with experience it can move quite quickly.”

The two researchers concluded an intriguing reference to a fossil species. They tracked down illustrations of the bivalve Bornia cookie from the paper describing the species in 1937. It seemed to match the modern one. If confirmed, this would mean that Goddard had not found a new species, but some kind of living fossil.

It is worth noting that the scientist who described the species, George Willett, estimated that it may have 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 Willett’s original specimen (now classified as Cymatioa cooki) from the Los Angeles County Natural History Museum. This object, called the ‘type specimen’, serves to define the species, so it is the ultimate arbiter in mussel identification.

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

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

He suspects that the clams arrived here on current as planktonic larvae, carried from the south during the marine heatwaves from 2014 to 2016. This has allowed many marine species to expand their range northward, including several that have been specifically documented at Naples Point. Depending on the animal’s growth rate and longevity, this could explain why no one had noticed C. cooki at the site before 2018, including Goddard, who has been working on slugs at Naples Point since 2002.

“The Pacific coast of Baja California has broad intertidal areas of boulders that stretch literally for miles,” Goddard said, “and I suspect down there, Cymatioa cooki probably lives in close contact with animals that burrow under those boulders.