Enlarge (credit: Hal Beral)

For many creatures, having a limb caught in a predator’s mouth is usually a death sentence. Not starfish, though—they can detach the limb and leave the predator something to chew on while they crawl away. But how can they pull this off?

Starfish and some other animals (including lizards and salamanders) are capable of autonomy (shedding a limb when attacked). The biology behind this phenomenon in starfish was largely unknown until now. An international team of researchers led by Maurice Elphick, professor of Animal Physiology and Neuroscience at Queen Mary University of London, have found that a neurohormone released by starfish is largely responsible for detaching limbs that end up in a predator’s jaws.

So how does this neurohormone (specifically a neuropeptide) let the starfish get away? When a starfish is under stress from a predatory attack, this hormone is secreted, stimulating a muscle at the base of the animal’s arm that allows the arm to break off.

Enlarge / The African Lungfish, showing it's thin, wispy fins. (credit: feathercollector)

When it was first discovered, the coelacanth caused a lot of excitement. It was a living example of a group of fish that was thought to only exist as fossils. And not just any group of fish. With their long, stalk-like fins, coelacanths and their kin are thought to include the ancestors of all vertebrates that aren't fish—the tetrapods, or vertebrates with four limbs. Meaning, among a lot of other things, us.

Since then, however, evidence has piled up that we're more closely related to lungfish, which live in freshwater and are found in Africa, Australia, and South America. But lungfish are a bit weird. The African and South American species have seen the limb-like fins of their ancestors reduced to thin, floppy strands. And getting some perspective on their evolutionary history has proven difficult because they have the largest genomes known in animals, with the South American lungfish genome containing over 90 billion base pairs. That's 30 times the amount of DNA we have.

But new sequencing technology has made tackling that sort of challenge manageable, and an international collaboration has now completed the largest genome ever, one where all but one chromosome carry more DNA than is found in the human genome. The work points to a history where the South American lungfish has been adding 3 billion extra bases of DNA every 10 million years for the last 200 million years, all without adding a significant number of new genes. Instead, it seems to have lost the ability to keep junk DNA in check.

Enlarge / A Sixgill Hagfish (Eptatretus hexatrema) in False Bay, South Africa. (credit: Peter Southwood/CC BY-SA 4.0)

The humble hagfish is an ugly, gray, eel-like creature best known for its ability to unleash a cloud of sticky slime onto unsuspecting predators, clogging the gills and suffocating said predators. That's why it's affectionately known as a "snot snake." Hagfish also love to burrow into the deep-sea sediment, but scientists have been unable to observe precisely how they do so because the murky sediment obscures the view. Researchers at Chapman University built a special tank with transparent gelatin to overcome this challenge and get a complete picture of the burrowing behavior, according to a new paper published in the Journal of Experimental Biology.

“For a long time we’ve known that hagfish can burrow into soft sediments, but we had no idea how they do it," said co-author Douglas Fudge, a marine biologist who heads a lab at Chapman devoted to the study of hagfish. "By figuring out how to get hagfish to voluntarily burrow into transparent gelatin, we were able to get the first ever look at this process.”

As previously reported, scientists have been studying hagfish slime for years because it's such an unusual material. It's not like mucus, which dries out and hardens over time. Hagfish slime stays slimy, giving it the consistency of half-solidified gelatin. That's due to long, thread-like fibers in the slime, in addition to the proteins and sugars that make up mucin, the other major component. Those fibers coil up into "skeins" that resemble balls of yarn. When the hagfish lets loose with a shot of slime, the skeins uncoil and combine with the salt water, blowing up more than 10,000 times its original size.