Huge Deep Sea Bug—Er, Isopod—Discovered in Gulf of Mexico

The newly described species can grow to one and a half feet long.

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The dorsal and ventral sides of a newly discovered giant isopod species.
The newly discovered isopod B. yucatanensis.
Photo: Dr Ming-Chih Huang, Journal of Natural History

Scientists recently trapped a giant isopod off the coast of Mexico, and after studying its anatomy and DNA, they determined that the crustacean is an entirely new species.

Deep sea isopods dwell on the seafloor and scavenge the carrion and marine snow that all dead things in the ocean become. In 2019, isopods in the Gulf of Mexico became famous when a video captured them devouring dead alligators intentionally sunk by scientists; in 51 days, all that was left of the reptiles’ carcasses were spines and skulls.

The recent study described Bathynomus yucatanensis, a giant isopod subspecies that can grow up to 1.64 feet from oblong head to rounded tail. The team’s work is published in the Journal of Natural History.

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“It is increasingly evident that species of Bathynomus may be exceedingly similar in overall appearance, and also that there is a long history of misidentification of species in the genus,” the researchers wrote.

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To the naked eye, that misidentification is understandable. Giant isopods scuttle around like massive animatronic grains of rice; it’s only when you flip them over that you can see their many legs and antennae.

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Relatives of terrestrial woodlice and the adorably named roly-polys (also known as pillpugs), giant isopods’ dorsal sides are sheathed in a plated exoskeleton. Their gigantism may be an adaptation to their abyssal habitat, a pattern seen in Japanese spider crabs, oarfish, and the largest squid species.

The research team compared the new isopod species to its nearest relatives in the Gulf. They found that B. yucatanensis is more slender and slightly shorter in length than its cousins, and it has more spines protruding from its tail.

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The newly discovered species is also yellower than its nearest relatives, which are more translucent white.

Genetic analysis also supported the new species designation, as the creature’s DNA was more like the giant isopod B. giganteus than the other species in the Gulf, B. maxeyorum.

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Besides identifying the new isopod, the researchers also showed that an isopod species in the South China Sea was historically misidentified as a species that lives farther south, in the Coral Sea off Australia.

The research complicates our picture of giant isopods; though the animals can be seen as a monolith, they have remarkable diversity in their ranks. Not all creepy crawlies are the same—but most of us probably aren’t looking closely enough to see their subtle differences.

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