Fossil Clam Species Found Living Off Southern California

by johnsmith

Cymatioa cooki, a species of small bivalve mollusk previously only known from the Pleistocene period, has been found living intertidally near Santa Barbara, California.

Cymatioa cooki. Image credit: P. Valentich-Scott & J.H.R. Goddard, doi: 10.3897/zookeys.1128.95139.

“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,” said Dr. Jeff Goddard, a researcher in the University of California, Santa Barbara.

“Ours doesn’t go back anywhere near as far as the famous coelacanth or the deep-water mollusk 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.”

In 2018 and 2019, Dr. Goddard and his colleague, Dr. Paul Valentich-Scott from the Santa Barbara Museum of Natural History, found three living individuals of small, translucent bivalves at Naples Point in Santa Barbara County, California.

“Their shells were only 10 mm long. When they extended and started waving about a bright white-striped foot longer than their shell, I realized I had never seen this species before,” Dr. Goddard said.

“I was surprised and intrigued. I know this family of bivalves (Galeommatidae) very well along the coast of the Americas. This was something I’d never seen before,” Dr. Valentich-Scott said.

The researchers examined their specimens from Naples Point and concluded they were not the same as Cymatioa electilis, the other living member of the Cymatioa genus recorded from the region.

With subsequent research, they determined the specimens matched the holotype of the extinct species Cymatioa cooki (also known as Bornia cooki) from the Pleistocene of Los Angeles County.

“This really started ‘the hunt’ for me,” Dr. Valentich-Scott said.

“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.”

“After carefully comparing the specimens from Naples Point with Cymatioa cooki, I concluded they were the same species. It was pretty remarkable.”

Given the small size, translucent shell, and cryptic habits of Cymatioa cooki, it is not surprising that living instances of the species have been overlooked for over 80 years.

“There is such a long history of shell-collecting and malacology in Southern California — including folks interested in the harder to find micro-mollusks — that it’s hard to believe no one found even the shells of our little cutie,” Dr. Goddard said.

The discovery is reported in the journal Zookeys.


P. Valentich-Scott & J.H.R. Goddard. 2022. A fossil species found living off southern California, with notes on the genus Cymatioa (Mollusca, Bivalvia, Galeommatoidea). ZooKeys 1128: 53-62; doi: 10.3897/zookeys.1128.95139

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