Science

Discovery of a new batin species off the Gulf of Mexico

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A large family of isopods forms an extremely diverse zoological order, including terrestrial and marine animals. With at least 10,000 different species, the family may have grown even larger with the discovery of a new species of the genus Bathynomus (giant isopods) off the Yucatan at depths of 600 to 800 meters. Although the specimen was found in the same area where Bathynomus giganteus was found, it differs morphologically and genetically. According to the authors of the discovery, Bathynomus yucatanensis, and probably several of its other cousins, may have gone unnoticed for a long time because the group would have been the victim of a long history of misidentification.

Batinomes are large and curious isopods, averaging the size of a soccer ball. They lived in the deep sea for 200 to 300 million years. The largest of them, Bathynomus giganteus, was discovered in the Gulf of Mexico by the famous explorer and zoologist Milne-Edwards in 1879. This “pill insect” is said to live at depths of more than 2,500 meters.

Bathynomus Yucatanensis was found in the same location as B. giganteus but is thought to be fundamentally different, according to a study done in collaboration with National Tainan University. It could even be two species combined into one by a common evolutionary advantage.

Morphological and genetic differences

Because the new species was found in the same location as B. giganteus, the researchers initially believed it was the same species. However, they found that the specimen had subtle morphological differences. B. yucatanensis is said to be thinner in proportion, with longer pectoral limbs and longer antennae, although it is smaller overall. Its dimensions are 26 cm versus 36 cm (length) for B. giganteus. This species would have eluded experts for a long time because it would have the same number of spines as B. giganteus, and this characteristic is often regarded as the main element in distinguishing batinome species between them.

Genetic analysis, which is currently being closely studied at the Enoshima Aquarium in Japan, confirmed the differences between the new specimen and B. giganteus. The sequences of the two genes (COI and 16S rRNA) will differ between the two species, the difference seems insignificant, but it is significant as it determines the batyn morphology. However, according to a new study detailed in the Journal of Natural History, their many similarities suggest a common ancestor.

Genetic sequencing also showed that other South China Sea specimens were misclassified, such as a specimen mistaken for B. kensleyi but actually B. jamesi. Because the 20 or so known species of batinome are very similar in many respects, these results may demonstrate the need to re-examine all species within the genus to confirm the accuracy of their taxonomy.

Equipped for extreme conditions

These living fossils, living mainly at great depths, could survive for a long time in extreme conditions. And although they are close to crabs and lobsters, unfortunately, we still know very little about them, since their habitat is often inaccessible to humans. They live, in particular, in areas of very high pressure (due to depth), thanks to their incredibly tough shell.

According to previous research, batynomes may even survive major extinction events as they can starve for years. Despite their intimidating appearance, experiments have shown them to have opportunistic behaviour, feeding profusely when the opportunity arises before preparing to fast again as food is scarce deep down.

Proving this behavior, researchers dumped an alligator carcass into the sea in the Gulf of Mexico in 2019. Some would eat so much that they would begin to drift. However, the mechanisms that allow them long periods of starvation remain unexplained.

Journal of Natural History.

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