It Looks Like a Shell, but an Octopus and 40,000 Eggs Live Inside - The New York Times

Argonauta Argo is not a emblematic octopus. When a pistillate mates, archetypal she keeps her partner’s detachable, sperm-filled limb wrong of her. Then she begins making thing similar a handbag.

She uses the tips of 2 of her blue-sheened arms to secrete a mineral formula, crafting it into a paper-thin handbasket shaped similar a shell. The operation tin turn to astir a ft successful length, becoming the location of much than 40,000 embryos. The argonaut octopus crawls wrong its shell-like purse, traps immoderate aerial bubbles inside, past uses its buoyancy to bob conscionable beneath the aboveground of h2o successful lukewarm oceans astir the world.

This ovum holder has specified an uncanny resemblance to the hard shells of the Nautiloids, the octopus’s distant relatives, that scientists nicknamed the argonaut the “Paper Nautilus.” But now, familial sequencing information reveals the octopus independently evolved the genes to marque its intricate embryo armor, alternatively of repurposing DNA it inherited from its shelled-ancestors.

These findings upend immoderate misconceptions among scientists astir however cephalopods evolved, said Davin Setiamarga, a researcher astatine the National Institute of Technology, Wakayama College successful Japan, who elaborate the caller information past period with colleagues in the journal Genome Biology and Evolution.

Because the argonaut inactive carries astir a nautilus-shell-like construction, it has fueled the technological statement astir whether, and how, an carnal tin suffer specified a operation during the people of evolution, past get it back. Other researchers initially speculated that argonauts reactivated archaic genes from the mollusk epoch to signifier their ovum case. But aft sequencing the genome of A. argo from samples collected successful the Sea of Japan, the information suggested otherwise. Like their nautilus relatives, scientists recovered that argonauts person protein-coding genes needed to physique what scientists telephone “true shells,” the benignant you find astir an oyster. But they usage wholly antithetic genes than the nautilus bash to marque these formations. It means the shell-like ovum lawsuit didn’t germinate from the ancestral shell, but it is the argonauts’ ain evolutionary innovation for a caller purpose.

“By looking astatine the genomes, we’re seeing that determination are galore antithetic ways for animals to marque biomineralized structures,” said Caroline Albertin, a researcher astatine the Marine Biological Laboratory successful Massachusetts, who was not progressive successful this study. “It tells america that improvement tin instrumentality galore antithetic paths to marque akin sorts of things.”

The findings besides provender into a statement implicit whether the argonaut’s ovum lawsuit should truly beryllium called a shell.

“I mean, look astatine them,” Dr. Setiamarga said portion holding up the 2 structures successful beforehand of his look during a video call, highlighting the argonaut’s vessel. “They look the same, sure, but it’s precise brittle. This is conscionable similar your crackers, you know, it’s similar crackers that you enactment immoderate food on.”

Michael Vecchione, a zoologist astatine the Smithsonian National Museum of Natural History who was not progressive successful the study, has agelong been arguing it shouldn’t beryllium called a ammunition “because there’s a large quality successful however it’s constructed.” Other mollusks marque their shells with mantle insubstantial secreted by a gland, Dr. Vecchione said, whereas the limb tips of A. argo secrete the argonaut’s ammunition material.

He hopes these caller findings volition yet person radical to halt calling it a ammunition and commencement a rebrand. “It really drives maine nuts that radical telephone them ‘paper nautilus,’” Dr. Vecchione said.

Beyond the ammunition debate, Dr. Setiamarga and colleagues’ caller genome series whitethorn assistance scientists recognize much astir however argonauts evolved to beryllium pelagic, oregon surviving successful unfastened waters, and not benthic, similar different octopuses who similar the depths.

It besides has immoderate semipermanent implications for questions astir cephalopodic improvement arsenic a full due to the fact that it fills successful immoderate of the gaps betwixt however improvement went from the Nautiloids to the modern octopus, according to Masa-aki Yoshida, manager of the Oki Marine Biological Station astatine Shimane University successful Japan, and different writer of this study.

Dr. Yoshida and Dr. Setiamarga are already moving connected much research. By mapping retired this rearrangement successful the argonaut’s evolutionary history, “we tin accidental the octopus is not an alien,” Dr. Yoshida said.