‘Velvety’ crabs discovered living inside a worm tube off Japan are a new species
Off the coast Okinawa Island in southwestern Japan, researchers equipped with scuba gear and suction pumps set out to investigate the muddy bottom of Kin Bay.
Just over 30 feet down, they came upon a large parchment tube worm with two crabs, smaller than a penny, living inside of its tube.
These tiny crustaceans are now confirmed to be a new crab species called Hexapinus okinawa, according to a study published Aug. 14 in the peer-reviewed journal Zootaxa.
The new species is believed to have a commensal relationship only with parchment tube worms in the Chaetopterus genus, according to the study. In these types of interspecies relationships, one species benefits while the other is neither helped nor harmed.
These tube worms are characterized by having large bodies and tubes, measuring just over an inch at their widest point. They are also known to inhabit “muddier bottoms in inner bays,” researchers said. The marine worms live inside of tubes made from a parchment-like secretion.
The new species is mostly closely related to Hexapinussimplex, which can be found in a different species of tube worm, according to the study.
According to researchers, Hexapinus okinawa has a trapezoidal body partially covered by dense hair-like structures called setae.
One pair of legs is almost entirely covered in these “velvety” hairs, while the others have separate tufts. The species has small eyes and “stout” claws fringed with the velvety setae, according to the study.
To date, Hexapinus okinawa is known to only exist in Kin Bay and Oura Bay, according to researchers.
The discovery marks the sixth species in the Hexapinus genus, all of which are found in the Indo-West Pacific, the study said. It also marks the first species believed to be endemic, or found nowhere other other than, Okinawa Island, which it was named after.
The research team included Taigi Sato, James Davis Reimer and Tohru Naruse.
This story was originally published August 18, 2025 at 2:21 PM with the headline "‘Velvety’ crabs discovered living inside a worm tube off Japan are a new species."
