Rare fossil clam discovered alive

A dazzling array of hues highlights the long-lost clam of Southern California. Credit: Jeff Goddard

It is always exciting to discover a new species, but it is even more thrilling to rediscover a species that was thought to be extinct due to the passage of time. A small bivalve, previously only known from fossils, was recently discovered living at Naples Point, just north of UC Santa Barbara. The finding is published in the journal Zookeys.

Jeff Goddard, a research associate at UC Santa Barbara's Marine Science Institute and co-author of the study, remarked, "It's not all that common to find a fossilized species alive, particularly in a region as well-studied as Southern California." "Ours doesn't go back nearly as far as the famous Coelacanth or the deep-water mollusk Neopilina galatheae, which represent an entire class of animals believed to have vanished 400 million years ago, but it does go back to the time of all those wondrous animals found in the La Brea Tar Pits," the author writes.

On a low tide afternoon in November 2018, Goddard was searching for nudibranch sea slugs at Naples Point when he noticed a pair of small, translucent bivalves. He stated, "Their shells were only 10 millimeters long." "When they extended and began waving a bright white-striped foot longer than their shell, I realized I had never before encountered this species." This astonished Goddard, who has spent decades in the intertidal habitats of California, including many years at Naples Point. He immediately stopped what he was doing to photograph the fascinating animals up close.

With high-quality images in hand, Goddard decided not to collect the rare-looking animals. He sent the images to Paul Valentich- Scott, curator emeritus of malacology at the Santa Barbara Museum of Natural History, after determining their taxonomic family. "I was surprised and intrigued," recalled Valentich- Scott. "I am very familiar with this bivalve family (Galeommatidae) along the coast of the Americas. I had never seen anything like this before."

He suggested a few possibilities to Goddard, but stated that he would need to examine the animal in person to make an accurate determination. Goddard then returned to Naples Point to retrieve his clam. But after two hours of combing a few square meters, he had yet to locate his prize. He would continue to miss the species numerous times.

In the tidepools of Naples Point, it takes a keen eye to spot the tiny clam (bottom center) sitting next to this chiton. Credit: Jeff Goddard

In March 2019, after nine trips and nearly giving up for good, Goddard turned over yet another rock and discovered the needle in the haystack: A solitary specimen, adjacent to a few small white nudibranchs and a large chiton. Valentich-Scott would finally obtain his specimen, and the pair could begin identification.

Valentich- Scott was even more astonished upon touching the shell. He was aware that it belonged to a genus with a single member in the Santa Barbara area, but this shell did not match any of them. It increased the possibility that they had discovered a new species.

"This initiated 'the hunt' for me," said Valentich-Scott. "When I suspect that something is a new species, I must comb through all scientific literature published between 1758 and the present. It can be a daunting task, but with practice, it can be accomplished relatively quickly."

The two scientists decided to investigate an intriguing fossil species reference. They located illustrations of the bivalve Bornia cooki in the 1937 paper that described the species. It resembled the contemporary specimen. If confirmed, Goddard would not have discovered a new species, but rather a living fossil.

George Willett, the scientist who described the species, estimated that he had excavated and examined approximately one million fossil specimens from the Baldwin Hills in Los Angeles. However, he never discovered B. cooki himself. Instead, he named it after Edna Cook, a Baldwin Hills collector who had discovered the two known specimens.

The original specimen used by George Willett to describe the species. Credit: Valentich- Scott and others

Valentich-Scott requested the original specimen (now classified as Cymatioa cooki) from the Los Angeles County Natural History Museum. This object, known as the "type specimen," serves to define the species, making it the definitive identifier of the clam.

Goddard discovered a second specimen at Naples Point: a single empty shell buried in the sand beneath a boulder. Valentich-Scott concluded that the specimens from Naples Point and Willett's fossil belonged to the same species after a thorough comparison. "It was quite extraordinary," he recalled.

Despite its diminutive size and cryptic habitat, this raises the question of how the clam evaded detection for so long. "There is such a long history of shell-collecting and malacology in Southern California, including people who are interested in the more difficult-to-find micro-mollusks, that it's hard to believe no one has even found the shells of our little cutie," Goddard said.

He suspects that the bivalves arrived here as planktonic larvae, transported from the south during marine heatwaves between 2014 and 2016. This allowed many marine species to expand their ranges northward, including a number of species documented at Naples Point. Depending on the animal's growth rate and longevity, this could explain why no one, including Goddard, who has studied nudibranchs at Naples Point since 2002, had observed C. cooki at the site prior to 2018.

Goddard stated, "The Pacific coast of Baja California has vast intertidal boulder fields that stretch for miles, and I suspect that Cymatioa cooki lives in close association with animals that burrow beneath these boulders."

Journal information: ZooKeys


Font Size
lines height