This Massive, Deep-Sea Roly Poly Can Go Years Without Food Thanks to a Huge Stomach and a Stolen Gene, Study Suggests

The deep sea has no shortage of unusual creatures, from methane-eating spiders to shape-shifting octopuses. Among them are giant isopods—essentially bowling pin-sized pill bugs. Some of these curious crustaceans can survive for more than five years between meals, a feat that has puzzled researchers, given the isopods’ massive size.

Now, they’ve learned that the secret behind some deep-sea roly polies’ impressive endurance comes from a combination of a large stomach and evolutionary thievery. Millions of years ago, the isopods’ ancestors stole an energy metabolism-related gene from a bacterium and transferred it into their own DNA. The findings, published in the August 6 issue of the journal Cell, offer new insight into how some organisms can survive in extreme environments.

Surviving at the bottom of the ocean is no easy task: it’s dark, cold, under high pressure, and there’s little food. Giant isopods scuttle around the seafloor at depths of up to nearly 7,000 feet in the Atlantic and Indo-Pacific oceans. The massive creatures, which are related to garden-variety pill bugs on land, can grow to 11 to 20 inches long.

To better understand what the researchers call the “paradox of deep-sea gigantism,” they examined the anatomy and genomes—complete sets of genetic instructions—of two giant isopod species that live at different depths. They collected Bathynomus jamesi specimens from nearly 3,000 feet below the surface in the South China Sea and B. doederleini from a depth of almost 1,000 feet in the East China Sea. The team also compared the giant isopods to the intertidal isopod Cleantiella isopus, gathered from Qingdao, China.

In 2022, researchers described a new species of giant isopod called Bathynomus yucatanensis. A specimen collected from Mexico’s Yucatán Peninsula in 2017 had been misidentified as a larger relative. Analyses revealed the deepest-dwelling isopod had a huge stomach that took up around two-thirds of the creature’s body cavity, proportionally much larger than the stomach of the other giant species.

The researchers suspect the cavernous compartment acts as a storage container. That means B. jamesi can gorge itself on food—generally scavenged bits of fish, crabs and dead organic matter—whenever it comes across tasty morsels and stockpile much of its meal in its body. What’s more, both B. jamesi and B. doederleini had a gene called ND1.