NEW YORK, NY.- The hagfish, a deep-sea scavenger about the size and shape of a tube sock, has the curious ability to smother itself in its own snot. The mucus is a defense mechanism, released into the water (or in one unfortunate incident, all over an Oregon highway) when the fish feels threatened. Once it hits seawater, a tiny amount of the ooze expands to 10,000 times its original size in a fraction of a second, forming a tenacious web of goo. A shark trying to take a bite of a hagfish will find itself suddenly unable to breathe, its gills clogged with the slime.

But the same is true of the hagfish itself, which finds the process of being captured by scientists late at night on boats in the black ocean a bit stressful. Juan Pascual-Anaya, a biologist at the University of Málaga in Spain who has spent summers collecting hagfish off the coast of Japan, recalls having to strip the elastic gel off the animals with his hands.

“We have to be removing the mucus all the time on the ship, or they will die,” he said.

All this mucus-handling was in pursuit of a rather deep evolutionary unknown: what the hagfish’s genome can tell us about the earliest vertebrates. The hagfish has no jaw, making it part of a group that diverged long ago from the ancestors of jawed vertebrates like ourselves.

Last week, Pascual-Anaya and other scientists reported in the journal Nature Ecology & Evolution that they have sequenced the genome of the hagfish, discovering evidence that jawless fishes probably diverged from those with jaws more than a half-billion years ago. The ancestors of hagfish tripled the size of their genome more recently than that, after they’d already split from the marine life that were our ancestors.

Genome duplications, or even triplications, can be important events in the existence of a species, Pascual-Anaya said. They can occur during the development of germ cells, the eggs and sperm of a species, which may divide and keep the extra genome that should have gone into another cell. Once a species has all that extra genetic material to work with — a fresh bin of evolutionary tinker toys — it may change in a number of ways, developing new functions for old genes.

Jawed vertebrates have had at least two genome duplications, and Pascual-Anaya and his colleagues were curious whether the hagfish showed evidence of them too. They discovered that one of these duplications must have happened before the two groups of vertebrates split — the hagfish genome has signs of it — but the other was most likely after the fork in the evolutionary road. What’s more, they confirmed a suspicion other scientists had raised, that an ancestor of both the hagfish and the lamprey, another jawless wonder, at some point tripled its genome.

What’s particularly intriguing, the team wrote, is that the effects of supersizing the genome don’t seem to lead to as much variety as one might expect. The jawless vertebrates have duplications and triplications, but they don’t show the wild abundance of body shapes found in jawed vertebrates, from fish to bird to giraffe to primate.

“We have this preconception that whole genome duplication will lead to more complexity,” Pascual-Anaya said. “What we say is it depends on the nature of the duplication, the lineage, the animals.”

There’s still much more work ahead to understand the hagfish genome. But with this new sequence in hand, researchers can begin to explore which genes are linked to particular traits in today’s animals. Perhaps the genome may even lead to a better understanding of just how the hagfish creates its signature slime.

Pascual-Anaya doesn’t get out into the field as much as he’d like. But he has fond memories of scraping goo off wriggling hagfish until they exhausted their mucus supplies and could be safely left alone to recover.

“It’s very ugly,” he said of the creature, “but I love it.”

This article originally appeared in The New York Times.