A species of clam thought to have been extinct for 40,000 years has been observed alive

spécimen vivant espèce fossile

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A bivalve mollusc, bapt Cymatio cookie, until now known only through fossils from the Pleistocene period. But this tiny shrimp was recently spotted alive on a sandy beach off the California coast.

In November 2018, while searching for sea slugs at low tide on Naples Point Beach, Jeff Goddard, a research associate at UC Santa Barbara’s Marine Science Institute, came face-to-face with a pair of curious little translucent bivalves. The latter had a white, shiny striped shell, barely 10mm and a long leg. Although southern California bivalve molluscs have been widely studied and documented, Goddard had never seen this species before.

After taking several pictures of these animals, without disturbing them unnecessarily, he sent these photos to Paul Valentich-Scott, curator emeritus of malacology at the Santa Barbara Natural History Museum, who was amazed. ” I am very familiar with this family of bivalves (Galiommatidae) of the coast of America. It was something I had never seen before », relate-t-il. Photos are not enough to accurately identify the animal, it is necessary to capture it for closer examination. But a few months later, after several attempts, Goddard found a specimen of this strange mollusk.

Similar to a fossil record

The two researchers were able to begin their identification work. The animal’s particularly distinctive shell raised the possibility that it was a new, previously undescribed species. To confirm this, Valentich-Scott scrutinized all the scientific literature published from 1758 to the present day. A fossil species, Described in 1937Two in particular have attracted the attention of researchers.

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Lateral (A) and ventral (B) view of live specimen taken from Naples Point (length: 7.4 mm). (c and d) Cymatio cookie In its natural environment. © P. Valentich-Scott et al.

Illustrations of bivalves Bornia Cookie, found in an article by paleontologist George Willett, that the shell they found was very similar. Note that Willett documented the mollusc fauna while installing a sewer line in the Baldwin Hills of central Los Angeles. The work uncovered 20 to 30 cm thick Pleistocene deposits with invertebrate and vertebrate fossils more than a meter below the surface. These deposits are between 36,000 and 28,000.

In his publication, the scientist identified a total of 296 species of molluscs and described two new species of Galliommetidae bivalves. Rochefortia rayana etc Bornia Cookie (Today Cymatio cookie), the researchers say. Willett named the species after Edna Cook, a shell collector who collected the specimens at the time.

type model
The type specimen used by George Willett to describe this species Bornia Cookie a 1937. © P. Valentich-Scott et al.

After comparing their mollusk to the original specimen described by Willett, housed at the Natural History Museum of Los Angeles County, the researchers concluded that it was indeed the same species. At the same time, Goddard found another specimen at Naples Point, an empty shell, which matched it perfectly. Bornia Cookie.

A search that will undoubtedly lead to other paradigms

Finally, researchers have so far found three living specimens of this species: two individuals observed in 2018 and a specimen captured in 2019. C. cookie Thus joining the list of “Lazarus taxa”, which includes species that were thought to be extinct and have since been rediscovered. ” Finding a living organism for the first time in the fossil record is not very common. », Goddard observed. How could this mollusc escape the observation of experts for so long? ” Southern California has a long history of shell collecting and malacology […] It’s hard to believe that no one has even found the shells of this tiny creature “, he added.

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Their preferred habitat is further south off the Baja California Peninsula, which may explain why no one notices them. C. Cookie Before. ” Given C. kuki’s small size, translucent shell, and cryptic habits, it is not surprising that the species has been neglected for over 80 years. “, write the researchers, thanks to their new description, other individuals of this species will undoubtedly be found soon, especially further south, along the coast of Mexico.

According to the two researchers, these clams emerged in the form of planktonic larvae by ocean currents from south to Naples Point, particularly during the ocean heat waves of 2014 to 2016. The species extends its distribution northward, especially at Naples Point for many of them.

Source: P. Valentich-Scott et J. Goddard, ZooKeys

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