The worm Paralvinella hessleri is bright yellow due to the accumulation of arsenic in its skin cells, where the toxin reacts with sulfide from vent fluids to form orpiment, an orange-yellow pigment. (Image credit: Wang H, et al., 2025, PLOS Biology, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)) SUMMARY
Name: Paralvinella hessleri
Habitat: Pacific Ocean
What it eats: bacteria and organic debris around hydrothermal vents.
Deep-sea creatures are uniquely adapted to life in extreme conditions, and the worm Paralvinella hessleri is no exception. Moreover, it can survive in high concentrations of toxic chemicals, such as arsenic, by producing its own venom.
Found only in the hottest hydrothermal vents of the western Pacific Ocean, including the Okinawa Trench and the Mariana Back-arc Trench, these worms reach a length of approximately 22 millimeters and live in protective tubes attached to the vents. Remarkably, P. hessleri is the only known animal capable of colonizing and reproducing in the acidic, metal-rich zones of these vents, where temperatures can reach approximately 320 degrees Celsius.
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These worms possess an unusual survival trick that allows them to withstand high concentrations of toxic arsenic and sulfide found in hydrothermal vents. In humans, arsenic exposure is linked to serious health problems, including cancer and neurological disorders. However, P. hessleri turns this danger into protection: it accumulates arsenic in its skin cells, where the toxin reacts with sulfide from the hydrothermal vents to form orpiment—a less harmful, but still toxic, mineral.
This vibrant yellow-orange substance, once known as “royal yellow,” was historically used by artists as a pigment until its toxicity was discovered. P. hessleri, which gets its yellow-orange hue from orpiment crystals, can accumulate so much arsenic that it constitutes nearly 1% of the worm's body weight.
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In a 2025 paper published in the journal PLOS Biology, the researchers who discovered the worms' survival strategy described the process as “fighting poison with poison.”
Commenting on the discovery, study co-author Hao Wang, a researcher at the Institute of Oceanology, Chinese Academy of Sciences, said he was “stunned” when he first saw the worms using a remotely operated vehicle.
“The bright yellow Paralvinella hessleri worms were unlike anything I'd ever seen, standing out vividly against the white biofilm and dark landscape of the hydrothermal vent,” he said in a statement. “It was hard to believe any animal could survive, let alone thrive, in such an extreme and toxic environment.”
TOPICS: Amazing Animals
Lydia Smith, Social Media Navigator, Science Writer
Lydia Smith is a health and science journalist who has worked for British and American publications. She is studying for a Master's degree in Psychology at the University of Glasgow and holds an MA in English Literature from King's College London.
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