New massive deep-sea isopod discovered in Gulf of Mexico: 2,500% larger than common forest

New Species of Bathonymus Deep-Sea Isopods

Image of Bathynomus yucatanensis. Credit: Dr. Ming-Chih Huang, Journal of Natural History

A massive, “creamy yellow” relative of the Woodlouse was found living at a depth of 600 to 800 meters (2,000 to 2,600 feet), off the Yucatan Peninsula.

Scientists have identified a new species of Bathonymusthe famous genera of deep-sea isopods whose viral internet fame has made them the most famous aquatic crustaceans since Sebastian de The Little Mermaid

There are about 20 living species Bathonymus, a mysterious and primitive group that inhabits the benthic zone of the ocean: its deepest reaches, rarely explored in person. Isopod crustaceans are only distantly related to their more familiar decapod relatives, crabs, shrimps and lobsters.

A group of researchers has just revealed the latest creature on this list: B. yucatanensis, a new species that is about 26 cm (10 in) long. This makes it about 2,500% larger than the common dimple. The scientists, from Taiwan, Japan and Australia, published their findings on August 9 in the peer-reviewed journal. Natural History Magazine.

Deep-sea isopods belong to the same group that contains terrestrial isopods known variously as woodle, pillbugs and roly polys. They feed on decaying matter and are probably familiar to anyone who has lifted a rock or dug in the garden. In fact, they look quite similar, but for their extraordinary size: the largest of them grows to almost 50 centimeters (20 inches). And, just like lice, although they may look a little scary, they are completely harmless to humans.

Its odd features and unusual dimensions have spawned endless memes and a wide variety of products celebrating its endearing weirdness, from stuffed toys to phone cases.

This finding of B. yucatanensis adds another addition to the isopod pantheon and brings the total known species of Bathonymus in the gulf of mexico to three—B. giganteus was described in 1879 and B. maxeyorum was described in 2016.

It was initially thought to be a variation of B. giganteus, one of the largest deep-sea isopods. However, closer examination of the specimen, which was caught in a baited trap in 2017 in the Gulf of Mexico on the Yucatan Peninsula about 600 to 800 meters (2,000 to 2,600 feet) down, revealed a series of of unique characteristics.

B. yucatanensis is morphologically different from both B. giganteus i B. maxeyorum“, say the authors.

Kept by the Enoshima Aquarium in Japan, the individual studied was subtly different from its relatives. “Compared to B. giganteus, B. yucatanensis has more slender body proportions and is shorter in total length… and the pereopods [thoracic limbs] they are more slender,” the researchers note. It also has longer antennae. Both species have the same number of pleotelson spines. These spines protrude from the end of the crustacean’s tail.

Bathynomus giganteus was discovered more than a century ago, and more than 1,000 specimens have been studied without so far suggesting a second species with the same number of pleotelson spines,” they add. “Surface examination, using only pleotelson spines, could easily result in specimens B. yucatanensis being misidentified as B. giganteus“.

“Compared to B. maxeyorumthe most distinctive feature is the number of pleotelson spines: 11 spines B. yucatanensis vs. 7 inches B. maxeyorum“.
The creamy yellowish coloration of the shell further distinguished it from its grayer relatives.

To be sure, the researchers performed a comparative molecular genetic analysis B. giganteus i B. yucatanensis. “Due to the different sequences of the two genes (COI and 16S rRNA), together with the differences in morphology, we identified it as a new species,” they write. The phylogenetic tree they built showed this B. yucatanensis as most closely related to B. giganteus.

B. giganteus is in fact the closest species B. yucatanensis“, say the authors. “This indicates that the two species probably had a common ancestor. Also, there may be others to discover as well Bathynomus spp. in the tropical western Atlantic.

The paper also clarifies that the South China Sea specimens are identified as B. kensleyi they are actually B. jamesi. B. kensleyi it is restricted to the Coral Sea off the coast of Australia.

“It is increasingly evident that the species of Bathynomus may be very similar in general appearance, and also that there is a long history of misidentification of species in the genus,” the authors warn.

They note that these newly established species distinctions have conservation implications. “Some species of Bathynomus with commercial potential have become the target of deepwater trawling,” they say. While giant isopods are only sporadically exploited, “for the management of Bathynomus fisheries, it is important to know precisely which species are being caught.”

Reference: “A new species of Bathynomus Milne-Edwards, 1879 (Isopoda: Cirolanidae) from the southern Gulf of Mexico with a redescription of Bathynomus jamesi Kou, Chen and Li, 2017 from off Pratas Island, Taiwan” by Ming-Chih Huang, Tadashi Kawai and Niel L. Bruce, 9 Aug 2022, Natural History Magazine.
DOI: 10.1080/00222933.2022.2086835

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