Study: Octopuses evolved from these sea creatures

By Mark Waghorn via SWNS

Octopuses evolved from shellfish, according to new research.

The eight-limbed creatures' mysterious origins have been traced back to a clam-like animal that lived hundreds of millions of years ago.

It looked like Argonauta argo - a species found in tropical and subtropical open seas.
Females have a protective, spiral casing which protects the eggs inside.

They resemble the commonly known pearly nautilus - a very distant relative which has a hard shell and thrives on the ocean floor.

The findings could help alien hunters. Octopuses are regarded as the closest thing to how alien life may have evolved.

A Japanese team has mapped the argonaut’s genome for the first time - shedding fresh light on shell evolution and egg case formation.

The researchers found the egg case protein-coding genes in argonauts and discovered most were not used to form shells in distantly related species, including the nautilus.

This suggests that while the distant ancestors of argonaut octopuses likely had shells, the shells didn’t evolve into egg cases.

"The argonaut genome is particularly intriguing because it shows that the break in synteny reported in the known octopus genome is not a general trait of this group," said corresponding author Dr. Davin Setiamarga, of Wakayama College.

"We have demonstrated that, contrary to popular belief, cephalopods do not necessarily exhibit a distinct genome evolution."

Unlike any other octopus, the female argonaut, which can be up to 20 inches in length, makes itself a paper-thin shell.

It secretes this shell, made of calcium carbonate, from two web structures on the sides of its body.

The males are much smaller, typically only a centimeter in length, and do not produce shells.

Octopuses are renowned for their intelligence. They can use tools, carry coconut shells for shelter, stack rocks to protect their dens and carry jellyfish tentacles for defense.

In captivity, they can learn to solve puzzles, open screw-top jars, and squirt humans they don't like. And they are as smart as your average dog.

The study reveals the genomic background of argonauts and shows how the species adapted to the open ocean and acquired its shell-like egg case.

Scientists previously had avoided targeting argonauts since it was difficult to keep the animals in aquaria for research purposes.

The authors here, however, had access to a location in the Sea of Japan ideal for acquiring fresh samples.

Setiamarga added: "We anticipate that our findings will further the research of metazoan, mollusk, and cephalopod genome evolution, which has remained largely unexplored thus far."

The study was published by the journal Genome Biology and Evolution.