Sea snails that have lost their shells and flap their wings through open ocean and found some interesting ways to stop themselves becoming someone else's dinner, as Rob Jennings, from the University of Massachusetts, explains...
Rob - So sea angels are a group of snails, basically. They're not too distant relatives of garden snails that you would find on land in your back yard.
Sea angels have evolved the behaviour of living in the water column. They're born swimming in the ocean, they grow up swimming in the ocean, and they spend all of their lives in the middle of the water never touching the bottom.
They are very beautiful animals. You know, they have these transparent bodies and these giant wings, they look a lot like angels. In a marine world where we've named things sea slugs, and we have sea lice, and we even have sea cucumbers I think it speaks to how beautiful they are that they've inspired the name sea angels.
As far as we know right now it looks like the marine snails that live on the bottom that have that normal sort of snail shell were the first kind to evolve and then they evolved so that they could live up in the water column but they brought their shell with them.
And over a lot of evolutionary time, there's evolution to loose this shell so sea angels are sort of the result of this evolution - these snail-like molluscs but without a shell anymore.
But one of the really interesting things is that in Antarctic waters Clione antarctica has developed this evolutionary tactic to sort of make up for the fact that it doesn't have a shell.
So, if you're swimming in the water column a shell is heavy, and it sort of pulls you down, but it also offers you protection, so you can retreat into your shell then it's very hard for anyone to eat you.
So these sea angels have lost that protective ability, but instead they've evolved, or at least Clione Antarctica has evolved bad tasting compounds that it synthesises. So, fish and other predators learn very quickly when they take a bite of Clione that it's not something that they want for a meal.
And this has led to actually a very curious interaction between sea angels and a totally unrelated group of animals, hyperiid amphipods, they're sort of distant cousins of shrimp and of krill.
And these amphipods have learned that if they grab onto a Clione and essentially hold is hostage and swim around carrying this giant sea angel on it's back, that fish and other predators won't eat the amphipod because it's got this bad-tasting Clione carried along with it.
So they sort of abduct Cliones and use them as protection and then will let them go after a time so the Clione can feed and stay alive itself, and then grab another Clione as soon as they can.