Researchers have identified a new species of Bathonymthe famous genus of deep-sea isopods whose viral fame on the Internet has made them the most famous aquatic crustacean since Sébastien de The little Mermaid.
There are about twenty living species Bathonym, a mysterious and primitive group that inhabits the benthic zone of the ocean – its deepest parts, rarely explored in person. Isopod crustaceans are only distantly related to their better known decapod relatives, crabs, shrimps and lobsters.
Publish their findings in the peer-reviewed natural history journala group of Taiwanese, Japanese and Australian researchers reveals the last creature on this list:B. yucatanensisa new species that is about 26cm long, about 2500% longer than the woodlouse.
Deep-sea isopods belong to the same group that contains the terrestrial isopods known as woodlice, woodlice, and roly polys, which feed on decaying matter and are likely familiar to anyone who has heaved a rock or dug in the garden. Indeed, they are quite similar, but for their extraordinary size – the largest of them reach almost 50 centimeters. And, just like woodlice, although they may look a bit scary, they are completely harmless to humans.
Their weird features and unusual dimensions have spawned endless memes and an array of products celebrating their endearing weirdness, from stuffed toys to phone cases.
This finding of B. yucatanensis adds another addition to the pantheon of isopods and brings the total of known species to Bathonym in the Gulf of Mexico at three—B. giganteus was described in 1879 and B. maxeyorum was described in 2016.
It was first thought to be a variant of B. giganteus, one of the largest deep-sea isopods. But closer examination of the specimen, which was caught in a baited trap in 2017 in the Gulf of Mexico off the Yucatán Peninsula at around 600 to 800 meters deep, revealed an array of unique characteristics.
“B. yucatanensis is morphologically distinct from the two B. giganteus and B. maxeyorum“say the authors.
Held by the Enoshima Aquarium in Japan, the individual studied was subtly different from his relatives. “Compared to B. giganteus, B. yucatanensis has more slender body proportions and shorter overall length… and pereopods [thoracic limbs] are more slender,” observe the researchers. It also has longer antennae. Both species have the same number of pleotelson spines. These spines protrude from the tail of the crustacean.
“giant bathynoma was discovered over a century ago, and over 1,000 specimens have been studied with no suggestion so far made of a second species with the same number of pleotelsonic spines,” they add. “A superficial examination, using only pleotelson spines, could easily result in specimens of B. yucatanensis to be misidentified as B. giganteus.”
“Compared to B. maxeyorumthe most distinctive feature is the number of pleotelson spines – 11 spines in B. yucatanensis against 7 in B. maxeyorum.”
The creamy, mottled yellow coloration of the shell further distinguishes it from its grayer relatives.
To be sure, the scientists conducted a molecular genetic analysis comparing B. giganteus and B. yucatanensis. “Due to the different sequences of the two genes (COI and 16S rRNA), coupled with differences in morphology, we identified it as a new species,” they write. The phylogenetic tree they constructed showed B. yucatanensis as most closely related to B. giganteus.
“B. giganteus is indeed the species closest to B. yucatanensis“say the authors. “This indicates that the two species probably had a common ancestor. Additionally, there may also be other undiscovered Bathynoma spp. in the western tropical Atlantic.
The document also states that specimens from the South China Sea identified as B. kensleyi are in fact B.jamesi. B. kensleyi is restricted to the Coral Sea off Australia.
“There is growing evidence that species of Bathynoma may be extremely similar in their general appearance, and also that there is a long history of misidentification of species within the genus,” the authors warn.
They note that these newly established species distinctions have implications for conservation. “Certain species of Bathynoma with commercial potential have become the targets of deep-sea trawling,” they say. While the giant isopods are only exploited sporadically, “for the management of Bathynoma fisheries, it is important to know precisely which species are caught.
– This press release was provided by Taylor & Francis Group