A creature whose relatives evolved roughly 500 million years ago - before dinosaurs, before trees - was sitting on the ocean floor off South Korea, misidentified as something it wasn’t. Two biologists conducting routine genetic analysis stumbled onto its true identity almost by accident.
The species is called Acanthochitona feroxa, and it belongs to one of the oldest surviving groups of animals on Earth.
A Case of Mistaken Identity
Acanthochitona feroxa is a chiton, a type of marine mollusk from the class Polyplacophora. If you’ve walked along a rocky shoreline and noticed a small, flat, oval-shaped creature clinging to a stone, you may have already encountered one. Chitons are distant relatives of snails, clams, and octopuses, distinguished by overlapping shell plates running down their backs.
For years, this particular chiton had been classified as a subspecies of Acanthochitona defilippii. The two look strikingly similar - their physical structures appear nearly identical to the naked eye. No one had reason to question the classification.
But Acanthochitona feroxa was its own distinct species all along.
How DNA Unmasked the Truth
Biologists Hyang Kim and Ui Wook Hang of Kyungpook National University in South Korea made the discovery while analyzing mitochondrial genomes of several Acanthochitona species. Mitochondrial DNA - the genetic instructions found inside the energy-producing structures within cells - evolves at a relatively consistent rate, making it a useful tool for measuring how closely or distantly related two organisms are.
Kim and Hang sequenced the mitochondrial genome of what turned out to be the new species and compared it to four other existing Acanthochitona species. Their findings were published in Marine Life Science & Technology.
“The findings of this study can provide foundational data for future molecular investigations into Acanthochitona, offering insights into the complete mitochondrial genomes of these five species and their phylogenetic relationships,” Kim and Hang said in the study.
Tiny Physical Clues, Visible Only Under a Microscope
Once researchers began looking more carefully, physical differences between feroxa and defilippii did emerge - but they required serious magnification.
Using scanning electron microscope analysis, the team observed differences in dorsal spicules on the shell. These tiny, thorn-like projections on the animal’s back were rounded in the new species rather than pointed. Differences also turned up in the radula (a tongue-like feeding structure common to mollusks) and in the shell plates themselves.
Combined with the molecular genetic analysis, these physical clues confirmed Acanthochitona feroxa as a distinct species.
“These molecular techniques have been proven potent in uncovering cryptic species within groups that exhibit morphological similarities,” the researchers said.
“Cryptic species” is a term for organisms that look virtually identical to another species on the outside but are genetically distinct enough to be classified separately. Genetic sequencing tools have made this concept increasingly relevant in biology, revealing that the natural world contains far more diversity than our eyes alone can detect.
What’s In a Name?
The species was identified from specimens collected off the southern and western coasts of South Korea. Its name, feroxa, comes from the Latin “ferox,” meaning “fierce” or “bristling” - a reference to the tufts along the edges of its flattened oval shell.
Chitons are estimated to have evolved around 500 million years ago. That predates dinosaurs by roughly 265 million years. It predates trees.
More than 1,300 chiton species are known today, and there are actually more living species than extinct ones. Approximately 940 known species have changed little over the last 300 million years, which has earned chitons a reputation as “living fossils” - organisms that have survived vast stretches of geological time with remarkably little physical change.
The broader group Polyplacophora began diversifying approximately 378 million years ago during the Devonian Period. The genus Acanthochitona - the specific group to which feroxa belongs - developed about 92 million years ago during the Late Cretaceous, when dinosaurs still roamed the Earth.
So while Acanthochitona feroxa is newly described by science, its family tree reaches deep into the past.
Production of this article included the use of AI. It was reviewed and edited by a team of content specialists.
