A tiny clam species known only from fossils is found alive in the tidepools of Santa Barbara
From: Currents
[at UC Santa Barbara]
By Harrison Tasoff
November 7, 2022 -- Discovering
a new species is always exciting, but so is finding one alive that everyone
assumed had been lost to the passage of time. A small clam, previously known
only from fossils, has recently been found living at Naples Point, just up the
coast from UC Santa Barbara. The discovery appears in the journal Zookeys.
“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 co-author Jeff
Goddard, a research associate at UC Santa Barbara’s Marine Science Institute.
“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.”
On an afternoon low
tide in November 2018, Goddard was turning over rocks searching for 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
extended and started waving about a bright white-striped foot longer than their
shell, I realized I had never seen this species before.” This surprised
Goddard, who has spent decades in California’s intertidal 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 appeared to be rare.
After pinning down 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,” Valentich-Scott recalled. “I
know this family of bivalves (Galeommatidae) very well along the coast
of the Americas. This was something I'd never seen before.”
He mentioned a few
possibilities to Goddard, but said he’d 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 combing just a few square meters, he still hadn’t
caught sight of his prize. The species would continue to elude him many more
times.
Nine trips later, in
March 2019, and nearly ready to give up for good, Goddard turned over yet
another rock and saw the needle in the haystack. A single specimen, next to a
couple of small white nudibranchs and a large chiton. Valentich-Scott would get
his specimen at last, and the pair could finally set to work on identification.
Valentich-Scott 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. It raised the exciting possibility that they had found a new
species.
“This really started
‘the hunt’ for me,” 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.”
The two researchers
decided to check out an intriguing reference to a fossil species. They tracked
down illustrations of the bivalve Bornia cooki from
the paper describing the species in 1937. It appeared to match the modern
specimen. If confirmed, this would mean that Goddard had found not a new
species, but a sort of living fossil.
It is worth noting that
the scientist who described the species, George Willett, estimated 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. Rather, he named it after Edna Cook, a Baldwin Hills
collector who had found the only two specimens known.
Valentich-Scott
requested Willett’s original specimen (now classified as Cymatioa cooki)
from the Natural History Museum of Los Angeles County. This object, called the
“type specimen,” serves to define the species, so it’s the ultimate arbiter of
the clam’s identification.
Meanwhile, Goddard
found another specimen at Naples Point — a single empty shell in the sand
underneath a boulder. After carefully comparing the specimens from Naples Point
with Willett’s fossil, Valentich-Scott concluded they were the same species.
“It was pretty remarkable,” he recalled.
Small size and cryptic
habitat notwithstanding, all of this begs the question of how the clam eluded
detection for so long. “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,” Goddard said.
He suspects the clams
may have arrived here on currents as planktonic larvae, carried up from the
south during marine heatwaves from 2014 through 2016. These enabled many marine
species to extend their distributions 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 C. cooki at
the site prior to 2018, including Goddard, who has worked on nudibranchs at
Naples Point since 2002.
“The Pacific coast of
Baja California has broad intertidal boulder fields that stretch literally for
miles,” Goddard said, “and I suspect that down there Cymatioa cooki is
probably living in close association with animals burrowing beneath those
boulders.”
https://www.news.ucsb.edu/2022/020757/needle-coastal-haystack
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