3 min readHere’s what you’ll learn when you read this story:
- A team of biologists just discovered a new species of chiton, a marine mollusk that clings to rocks and feeds on algae.
- Acanthochitona feroxa is a spiky, armored sea creature that genetic analysis revealed is a species of its own, rather than a subspecies as initially believed.
- With more species of chitons alive than extinct, it is thought others remain to be discovered.
With shells resembling plates of armor, chitons look like mollusks’ answer to isopods and trilobites. Chitons (class Polyplacophora) are one of Earth’s most venerable life-forms, having evolved around 500 million years ago, so they are often referred to as living fossils. With over 1,300 species known so far, they’re found just about everywhere on Earth, and remarkably, more of those species are extant than extinct. Now scientists have identified a new one.
Acanthochitona feroxa joins the 940 known species of chiton that have barely changed over the last 300 million years. The name of this living armored shield is derived from the Latin ferox, which translates to “fierce” or “bristling” and was inspired by the tufts that make chewing on this creature a rather unpleasant experience for predators. Usually found clinging to rocks, chitons of the genus Acanthochitona are recognizable by the tufts of bristles protruding from the edges of their flattened oval shells.
Chitons are usually identified morphologically. This can be problematic because it allows for taxonomic errors—variations in their physical traits sometimes mislead scientists. But by analyzing the mitochondrial genome of several Acanthochitona species collected off the southern and western coasts of South Korea, biologists Hyang Kim and Ui Wook Hang of Kyungpook National University in Korea were able to spot a new species hiding among their specimens. They sequenced its mitochondrial genome—dependable because they show how mutations spread through a population in a relatively short amount of time—and compared it to those of the other four existing Acanthochitona species.
“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 a study recently published in Marine Life Science & Technology.
Some visible features of A. feroxa occur throughout Polyplacophora. Chitons typically have pointed spicules on the backs of their shells and eat with a radula, a tonguelike structure covered in tiny sharp teeth that help them scrape algae off rock surfaces, though they also feed on microorganisms like diatoms and bryozoans. Previously thought to be a subspecies of Acanthochitona defilippii because of morphological similarities, the slightly different dorsal spicules observed on the shell of A. feroxa raised questions. Zooming in with a scanning electron microscope revealed that these were rounded instead of pointed, and its radula and shell plates showed geometric differences. Molecular genetic tools sealed the case that it was a new species. “These molecular techniques have been proven potent in uncovering cryptic species within groups that exhibit morphological similarities,” the researchers said.
There is a reason A. feroxa, with its brownish-greenish shell and distinguishing tufts, could almost pass for A. defilippii. The two are closely related even without one being a subspecies of the other. Polyplacophora began to diversify around 378 million years ago during the Devonian Period, at the same time proto-tetrapods (our earliest land ancestors) were emerging from the seas. The genus Acanthochitona developed about 92 million years ago, during the Late Cretaceous, when rising sea levels and spreading shallow marine habitats are thought to have created more niches for mollusks, including chitons, which have adapted to both the shallows and depths.
It’s likely that more new chiton species will be discovered. These living fossils have had eons to diversify, which makes it easy to imagine they come in forms nobody has imagined yet. They’re almost certainly out there right now, blending in with rocks, just waiting to be found.
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Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.