A tiny limpet reveals big secrets

The discovery represents a significant find in the study of the deep ocean, the largest ecosystem on the planet but one that is inhospitable to humans and remains largely unexplored. During a 2023 expedition aboard the E/V Nautilus, scientists using the remotely operated vehicle Hercules spotted a fragment of sunken wood resting off the remote Johnston Atoll.

As they drew closer, they found a thriving community that included a large population of strange limpets — oval, pale, and thick-shelled, with a distinctive arched profile. It didn’t take long for Paula Rodríguez-Flores, postdoctoral researcher in the Department of Organismic and Evolutionary Biology, to recognize a new species.

In a new study published in Molluscan Research, researchers in OEB and the Harvard Museum of Comparative Zoology formally describe Pectinodonta nautilus, named in honor of the exploration vessel responsible for its discovery. Gonzalo Giribet. The team led by Gonzalo Giribet, a professor of organismic and evolutionary biology and director of the MCZ, and Rodríguez-Flores used cutting-edge imaging and molecular techniques to examine the 79 individuals collected from the 35-centimeter-long piece of wood.

Belonging to a family of mollusks known as Pectinodontidae, P. nautilus is part of a rare group of limpets that make their homes on “wood falls”— tree trunks and branches that drift down from the surface and settle on the seafloor.

“Wood falls are fleeting ecosystems in the deep ocean, and yet they host remarkably specialized fauna,” said Rodríguez-Flores. “Unlike the well-studied ecosystems built around hydrothermal vents and methane seeps, wood falls remain elusive, less studied in their natural setting.” Back in the lab with the samples, the researchers used high-resolution micro-CT scanning and 3D modeling to visualize the limpets’ anatomy without dissection.

These limpets are large for their family — some more than three centimeters long — and they continue growing as the wood decays around them. Their off-white shells are sturdy, strongly arched, and unusually smooth. Scanning electron microscopy revealed a faint radial sculpture near the posterior dorsal surface. The smoothness, combined with thick concentric growth lines, set the species apart from their relatives.

This model is made from a scan of an Eoperipatus velvet worm. Graduate student Lily Shapiro and Giribet discovered this species in Singapore in 2025. Things got even more interesting inside their mouths. Like other wood-dwelling limpets, P.

nautilus boasts oversized radular teeth – the chitinous scraping tools that function like conveyor-belt tongues. Each tooth resembles an inverted V studded with around 17 cusps. When compared with relatives like P. mazuae, this new species has nearly double the size in radular structures, hinting at distinct feeding strategies or evolutionary pressures tied to their isolation.

DNA sequencing and mitochondrial genome analysis confirmed that P. nautilus represents a distinct lineage within Pectinodonta. Phylogenetic analyses revealed that P. nautilus is most closely linked with species from New Zealand and the Western Pacific, including P.

marinovichi and P. orientalis. “Our findings suggest this lineage of wood-fall may be far more widespread across the Pacific than previously recognized,” said Giribet. The deeper evolutionary tree, however, remains hazy.

Mitochondrial arrangements across related families showed intense gene shuffling, making lineage boundaries difficult to pin down. The researchers determined a need for full genome assemblies before confidently rewriting the family history. The findings also indicate that radular morphology, rather than shell shape, may be a more reliable way to distinguish among these cryptic species. “The discovery underscores how little is known about life in the deep sea,” Rodríguez-Flores said.

“Fewer than 7 percent of described marine species come from below 1,000 meters, leaving vast stretches of ocean biodiversity unexplored.” But the presence of individuals of many different sizes – juveniles to well-grown adults – indicates the wood fall supported multiple generations, suggesting that even tiny islands of habitat can sustain deep-sea communities long enough for population turnover and dispersal. Still, the research team, which included Arianna Lord, a Kenneth C. Griffin Graduate School of Arts and Sciences student, and Jennifer Winifred Trimble, MCZ curatorial associate, says that the discovery of P. nautilus adds a crucial piece to the puzzle of how life persists in one of Earth’s harshest habitats.

“Every deep dive reveals that the ocean still holds countless surprises,” said Rodríguez-Flores. “We’re only just beginning to understand the hidden biodiversity living on the seafloor.”