New Species of Deep Sea Isopod Discovered

The giant crustacean was originally mistaken for a different species at an aquarium in Japan

Front and back view of the new giant isopod species
A new species of giant isopod, Bathynomus yucatanensis Huang et al. via Journal of Natural History

Giant isopods are like something out of a science fiction novel—these massive, armored crustaceans use 14 legs to crawl along the ocean floor at staggering depths. It might seem unlikely that one of these species could be missed while in plain sight, but that’s exactly what’s happened, until now. Scientists have discovered a new giant isopod species among the sea creatures held in a Japanese aquarium.

This cream-colored crustacean was originally mistaken for its larger relative, called Bathynomus giganteus. Then, while researching isopod genetics, Huang Ming-Chih from Taiwan’s National University of Tainan sequenced its DNA. The genetic sequence showed at least 35 differences between B. giganteus and this isopod, which meant this individual appeared to be something new.

“At first, I thought it was [genetic] contamination, so I repeated the [DNA] sequencing experiment several times,” Huang tells New Scientist's Corryn Wetzel. “The results were the same.” 

Huang and two other experts describe the new isopod in a study published in the Journal of Natural History. They dubbed it Bathynomus yucatanensis, after Mexico’s Yucatán Peninsula, where it was captured in 2017.

Around 20 living Bathynomus, or giant isopod, species are known, but they are rarely seen by humans because they live so deep in the ocean. Before being housed at the Japanese aquarium, the B. yucatanensis specimen was collected between about 1,970 and 2,625 feet below sea level, per a statement.

B.yucatanensis looks like its land-dwelling isopod relative, the common woodlouse (also called a pill bug or roly poly)—but at 10 inches long and 5 inches wide, B. yucatanensis is about 25 times larger.

The authors constructed an evolutionary tree, mapping the relationships between this and other isopods. They found that the closest relative of the new-to-science B. yucatanensis is the larger B. giganteus—the isopod that it was originally mistaken for. “The two species likely had a common ancestor,” the researchers write.

Compared to B. giganteus, this new species “has more slender body proportions and is shorter in total length,” the authors write. Plus, it has longer antennae and a thorax that’s shaped like an inverted triangle, rather than an oval.

The researchers suggest there may be other Bathynomus species still undiscovered in the Gulf of Mexico. As of now, though, this finding brings the total to three—B. maxeyorum, which was described in 2016, B. giganteus and B. yucatanensis

Being able to identify these species could be important to conservation: The researchers conclude that some giant isopods are targets of deep-sea trawl fisheries, so “it is important to know precisely which species are being caught.”

Besides, the new discovery gives scientists a clearer picture of what’s out there on the ocean floor. "The ecological diversity of the Gulf of Mexico may be more complex than [previously] thought," Huang tells Live Science's Patrick Pester in an email.