A new species of chiton — a tiny, armored marine mollusk from a lineage roughly 500 million years old — has been identified off the coast of South Korea after routine genetic analysis revealed it was not the already-known creature researchers assumed it to be.
The species, named Acanthochitona feroxa, was collected from the southern and western coasts of South Korea. It had previously been considered a subspecies of Acanthochitona defilippii because the two look nearly identical to the naked eye.
It took mitochondrial genome sequencing and scanning electron microscopy to tell them apart.
What chitons are
Chitons are flat, oval-shaped marine mollusks belonging to the class Polyplacophora. They carry eight overlapping shell plates on their backs and cling to rocks in coastal waters around the world. They’re estimated to have evolved around 500 million years ago.
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More than 1,300 chiton species are known to science, and more extant species exist than extinct ones. Approximately 940 known species have changed little over the last 300 million years, earning them the label “living fossils.”
Polyplacophora began diversifying approximately 378 million years ago during the Devonian Period. The genus Acanthochitona, to which the new species belongs, developed about 92 million years ago during the Late Cretaceous.
How the discovery happened
Biologists Hyang Kim and Ui Wook Hang of Kyungpook National University sequenced the mitochondrial genome of the newly identified species and compared it to four other existing Acanthochitona species. The results diverged from expectations.
Scanning electron microscope analysis showed the dorsal spicules on the shell were rounded rather than pointed. Differences were also identified in the radula — the feeding structure — and the shell plates. Molecular genetic analysis confirmed it as a distinct species.
Their findings were published in Marine Life Science & Technology.
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“These molecular techniques have been proven potent in uncovering cryptic species within groups that exhibit morphological similarities,” the researchers said.
The species name carries meaning. Feroxa comes from the Latin “ferox,” meaning “fierce” or “bristling,” a reference to the distinctive tufts along the edges of its flattened oval shell. Even among creatures that look alike at first glance, this one had a subtle visual signature hiding in plain sight.
Why it matters beyond one species
The discovery belongs to a growing category in biology: cryptic species, organisms that look nearly identical to known species but turn out to be genetically distinct.
The researchers framed their work as a foundation for broader investigation. “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.
Chitons are a particularly rich testing ground for this kind of work. With 940 species showing minimal physical change over 300 million years, the gap between what they look like and what their genomes reveal could hold a significant number of undiscovered species.
The find reframes what “living fossil” means in practice. An animal can look the same for hundreds of millions of years and still be branching into distinct species at the genetic level. The stability is on the surface. Underneath, evolution is still working.
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