Are the ancestors of octopuses actually more like squids? The story of octopuses and squids connected by the vampire squid

"The Vampire That Doesn't Suck Blood" Takes Center Stage in Evolution

A creature draped in a black and red cloak gently drifts through the darkness of the deep sea.
Despite its ominous name, the "Vampire Squid," these creatures do not suck blood at all. Instead, they diligently collect and consume "marine snow," the debris floating in the ocean, acting as gentle cleaners of the sea.Wikipedia

Now, the vampire squid is stepping into the spotlight of evolutionary biology.
An international team, including the University of Vienna, National Institute of Technology, Wakayama College, and Shimane University, has precisely decoded the genome of this creature, presenting results that strongly suggest that the common ancestor of octopuses and squids was more "squid-like" than "octopus-like."Phys.org

The "In-Between" Existence of the Vampire Squid

The Japanese name for the vampire squid is not yet established, but it is often referred to as "Koumori-dako" in Japanese, meaning "bat octopus," as introduced by the lead researcher, Masaaki Yoshida.Phys.org

• Eight Arms Like an Octopus

• However, the bat-like membrane connecting its arms and the remnant of a shell (gladius) inside its body are closer to those of a squid.

• Ecologically, it doesn't closely resemble either octopuses or squids, being a "low-energy detritus feeder" specialized for the low-oxygen environment of the deep sea.

Thus, both morphologically and ecologically,it has been noted for possessing intermediate characteristics between octopuses and squids.Wikipedia

This study sheds light on such an "in-between existence" from the genomic level.

11 Billion Base Pairs, One of the Largest Cephalopod Genomes

The research team assembled the vampire squid's genome at the chromosome level, revealing that its total length exceeds11 billion base pairs—about four times that of humans, making it the largest among cephalopods analyzed to date.

However, the surprise is not just in its size.
Typically, when a genome becomes larger, the structure of chromosomes tends to become complexly shuffled. Yet, in the vampire squid,the arrangement of chromosomes remarkably preserved the "ancient type," similar to more primitive squids and cuttlefish.univie.ac.at

Researchers have thus positioned the vampire squid as a "genomic living fossil."univie.ac.at

The Octopus Genome Was Formed by "Fusion and Shuffling"

So, how does the genome of modern octopuses differ when compared to the vampire squid?

The team also compared the genomes of other octopus relatives, such as the pelagic "Argonauta hians," and concluded thatthe octopus chromosomes were reorganized from a squid-like ancestral genome through a process called "fusion-with-mixing."univie.ac.at

This means that not only did chromosomes simply attach,

• multiple chromosomes fused

• and gene rearrangements occurred within them

• creating a new "chromosome map."

This dynamic reconstruction is believed to have led to the rapid evolution of the octopus's unique soft body, dexterous arms, and shell-less lifestyle.
univie.ac.at

The key point of the research is that evolution was driven not by "the invention of new genes" but by "the diversification resulting from the rearrangement of existing genes at the chromosome level."

Was the Common Ancestor a "Squid-Like Octopus"?

Traditionally, the phylogenetic relationship between octopuses and squids was estimated from fossil records and morphological comparisons, suggesting that octopuses emerged from a squid-like ancestor with degenerated shells, but the details were unclear.Wikipedia

With the acquisition of the "intermediate" genome of the vampire squid, the following story has taken a more concrete shape.

1. About 300 million years ago, there existed a common ancestor of octopuses and squids (a squid-like cuttlefish-like animal).

2. From there,

   • Decapodiformes (squids and cuttlefish): Maintained relatively ancestral chromosome structures

   • Octopodiformes (octopuses and vampire squid): Among them, octopuses acquired "octopus-like" morphology through large-scale chromosome reorganization

3. The vampire squid still retains the intermediate chromosome structureas a genomic intermediate species

In other words, **"The ancestors of octopuses were more squid-like than previously thought."**univie.ac.at

The Victory of "Energy-Saving Design" Hidden in the Deep Sea

The vampire squid itself is a sufficiently strange and fascinating creature, even without the evolutionary story.

• About 30 cm in length

• Inhabits the deep sea at depths of 600-900 meters in temperate to tropical regions worldwide, within the "oxygen minimum zone" where there is almost no oxygen

• Lives an "energy-saving lifestyle," drastically reducing metabolism while slowly drifting and collecting marine snow to eat

• When sensing danger, it turns its cloak inside out to become a spiky "pineapple shape" and scatters glowing blue-green mucus to confuse predators

This is an incredible array of adaptations.Wikipedia

The deep-sea environment is said to have remained largely unchanged for 300 million years.
Therefore, it can be viewed that the ancestors of the vampire squid, which escaped into the deep sea, experienced "slow-motion" evolution at the chromosomal level due to the stable environment.Wikipedia

In other words, it results in two contrasting success patterns emerging from the same cephalopod lineage: **"The rapidly evolving octopus" and "the vampire squid that fit perfectly into its environment and didn't need to change."**

On Social Media: "Lovecraftian" or "Definitely Extraterrestrial"?

This news has been disseminated worldwide from science and biology news sites like Phys.org and university press releases, gradually spreading on social media platforms like X (formerly Twitter) and Threads.Phys.org

On X, science accounts have

• posted with links, calmly introducing "#Research Vampires in the deep, an ancient link between octopuses and squids."X (formerly Twitter)

• Threads explaining "a 'genomic living fossil' has been found" and "a direct link between octopuses and squids"

are being retweeted, especially among researchers and enthusiasts.

Meanwhile, in communities of deep-sea life enthusiasts and on Reddit, where past "vampire squid" videos have been popular,

• comments like "Cephalopods are almost 'alien' on Earth after all"

• and "Despite looking straight out of a Lovecraft story, all it does is clean the ocean"

are common, with many expressing surprise at the gap between its horror-like appearance and eco-heroic nature.Reddit

In the Japanese-speaking world, there are positive reactions such as "The name Koumori-dako is appealing" and "It's irresistible news for those who love both octopuses and squids," making it a topic that spreads easily due to its strong visuals and name, despite its specialized content.

From "Number of Genes" to "Design of Chromosomes" in Evolution

What makes this research unique is its shift in perspective from "the invention of new genes" as the driving force of evolution to"rearrangement at the chromosome level."

Even with the same genome content,

• the position of genes on which chromosome

• and when genes placed close together work together

can greatly change the appearance of an organism.
The remarkable intelligence and dexterity of octopuses may also be supported more by changes in this "wiring diagram" than by the gene set itself.Discover Magazine##HTML_TAG_453