The Argonaut Argo is not an octopus as usual. When the female copulates, she holds the first part of the penis, the sperm part inside her. Then he begins to make something like a purse.
He uses two blue arms with very shiny tips to hide the mineral formula, and it is in thin paper baskets shaped like shells. The structure can grow up to a foot in length, housing more than 40,000 embryos. The Argonaut octopus crawls inside its shell bag, traps some air bubbles inside, then uses its buoyancy to scurry beneath the surface of the water in the warm oceans around the world.
This egg holder bears such an unusual resemblance to the hard shells of Nautiloids, relatives of octopuses, that scientists have dubbed the argonaut the “Paper Nautilus.” Now, however, genetic sequencing data shows that the octopus independently evolved the genes to make its own intricate embryonic armor, replacing the DNA it had inherited from older crustaceans.
These findings have caused some confusion among scientists about how cephalopods evolved, said Davin Setiamarga, a researcher at the National Institute of Technology, Wakayama College in Japan, who published the new data last month with colleagues in the journal Genome Biology and Evolution..
The last common ancestor of all cephalopods probably had a chambered, pearly shell, not unlike the iconic nautilus-clad, shell-like cephalopod that still survives today. But over millions of years of evolution, soft cephalopods such as polyps, squids and cuttlefish evolved to that inner shell and shrink it as they adapted to their individual habitats. That’s why when you think octopus, squishy (although there are some exceptions, like ram’s horn squid).
Since the argonaut still carries around the construction of shells, the scientific debate about whether and how an animal can lose such a structure through evolution can regain it. Other researchers initially thought that the Argonauts had reactivated archaic genes from the mollusk era to form their egg case. But after sequencing the genome of A. argonis from samples collected in the Sea of Japan, the data suggested otherwise. Like their marine relatives, scientists have discovered that argonauts have protein-coding genes needed to make what scientists call “true shells,” the kind you find around oysters. But they use a completely different species than the nautilus to make these forms. It means that the egg shell did not develop by chance from the shell of an ancestor, but it is a characteristic of the evolution of the argonauts for a new purpose.
“When we look at the genomes, we see that there are many ways for animals to make biomining structures,” said Caroline Albertin, a researcher at the Marine Biological Laboratory in Massachusetts, who was not involved in this study.
The findings also feed into the debate as to whether the case of the argonaut egg should really be called a shell.
“Wait,” said Dr. Setiamarga said, holding the two structures in front of his face while calling the video, highlighting the Argonaut vessel. “They look the same, but it’s very fragile. This is like your crack, you know, that’s like the crack that you put some cheese on.
Michael Vecchione, a zoologist at the Smithsonian’s National Museum of Natural History, who was not in the study, has long argued that it should not be called a shell because the major difference is how it is constructed. Other skeletons make their shells with the mantle tissue secreted by the bullet, Dr. Vecchione said, when the tips of the arms of A. argo hide the material of the argonaut’s shell.
He hopes the new findings will finally convince him to stop calling it a shell and start rebranding. She pushes me nuts, which they call paper nautilus, Dr. Vecchione said.
Outside of the test discussion, Dr. Setiamarga and colleagues’ new genome sequence is helping scientists better understand how argonauts evolved to be pelagic, or living in open water, and not benthic, like other polyps that prefer the deep.
It also has long-term implications for questions about cephalopod evolution as a whole, because it fills in some of the gaps between how evolution went from nautiloids to the modern octopus, according to Masa-aki Yoshida, director of the Oki Marine Biological Station. at Shimane University in Japan and another author of this study.
Dr. Yoshida and Dr. Setiamarga now needs more research. Mapping this exchange in the history of the evolution of the argonaut, “we can say that the octopus is not alien,” said Dr. Yoshida.
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