A giant armoured crustacean kept in a Japanese aquarium has been found to be a new species. The discovery adds to the nearly two dozen known species of giant isopods – large, 14-legged crustaceans that relish the deepest, darkest, coldest waters of the Atlantic, Pacific and Indian Oceans.
When the yellow crustacean was collected from a baited trap off the coast of Mexico’s Yucatán Peninsula in 2017, it was assumed to belong to the Bathonymus giganteus species of isopod and was purchased by the Enoshima Aquarium in Fujisawa, Japan. The imposter avoided discovery until Huang Ming-Chih at the National University of Tainan in Taiwan decided to sequence the preserved specimen’s DNA for a previous project on isopod genetics.
Huang was surprised to see substantial differences between the new isopod’s genome – its full set of genetic instructions – and that of B. giganteus.
“At first, I thought it was [genetic] contamination, so I repeated the [DNA] sequencing experiment several times, and the results were the same,” says Huang, which suggested that he had two different species on his hands.
The new-to-science Bathonymus yucatanensis resembles a scaled-up version of its smaller cousin, the common woodlouse, or “pill bug”. The isopod, which is roughly the size of a 2-litre drinks bottle, lives about 600 to 800 metres below sea level in the rarely explored benthic zone.
Upon closer examination, Huang and his collaborators also pinpointed a handful of features that make B. yucatanensis unique. The specimen measures 26 centimetres from head to tail and is 13 centimetres wide.
“Compared to B. giganteus, B. yucatanensis has more slender body proportions and is shorter in total length than B. giganteus,” the authors write.
Extra-long antennae and a milky-yellow shell also help it stand out from its greyer peers.
Despite an intimidating, prehistoric appearance, B. yucatanensis is harmless to humans and prefers to scavenge on dead whales and fish that settle on the seabed.
Because B. yucatanensis was unrecognised for so long, Huang suspects other giant isopods may have also been misidentified. He says he is already investigating if a similar crustacean from the South China Sea is a new species, suggesting the list of giant isopods will continue to grow.
Journal reference: Journal of Natural History; DOI: 10.1080/00222933.2022.2086835
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