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Lurking deep in the ocean is a crimson, many-limbed beast known as Vampyroteuthis infernalis—the “vampire squid from hell.” Despite its theatrical name, this seldom-seen cephalopod is a scavenger, feeding on detritus with the help of its cloaked arms. Unsurprisingly, it’s not a vampire (or from hell). More surprisingly, it’s not a squid either.
With its squidlike appearance and eight arms like an octopus, the vampire squid doesn’t fit neatly into either group. Instead, it’s a kind of living fossil, representative of the primordial ancestors of both lineages. Now, for the first time, researchers have decoded the vampire squid’s genome—and they found plenty of surprises. They recently published their findings in iScience.
“The vampire squid sits right at the interface between octopuses and squids,” study author Oleg Simakov from the University of Vienna said in a statement. “Its genome reveals deep evolutionary secrets on how two strikingly different lineages could emerge from a shared ancestor.”
Read more: “What It Feels Like to Be an Octopus”
The biggest secret the vampire squid was hiding is just how massive its genome is: 11 billion base pairs, or gigabases. (A whopping 62 percent of their genetic material consists of non-coding repetitive elements, DNA sequences that repeat, but aren’t translated into proteins.) To give a bit of perspective, the vampire squid’s giant genome is nearly four times larger than the human genome and more than double the size of the largest known squid genome. Octopuses, on the other hand, have much smaller genomes, between two and three gigabases, something researchers say was key to their evolution.
Comparing the vampire squid’s genome to contemporary cephalopods, the team found that the vampire squid’s chromosomes more closely resembled those of squids, suggesting that the ancestors of all cephalopods were more squidlike than octopuslike. When they split off from their ancestors some 300 million years ago, octopuses underwent a sort of chromosomal fusion and mixing, resulting in smaller genomes, fewer chromosomes, and likely contributing to the evolution of specialized appendages. Rather than the emergence of new genes, researchers said, it’s this chromosomal rearrangement that drove the evolution of octopuses.
It’s a fascinating glimpse into the evolution of some of the most mysterious creatures on Earth. Who knows what secrets they’ll share with us next. 
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Lead image: © Citron / Wikimedia Commons
