Thanks to the Monterey Bay Aquarium and their research and technology partner MBARI
for partnering with us on this episode of SciShow.
They are super excited for folks to learn about
the deep sea. [ intro ]
In ocean waters around the world, from the poles to the tropics,
you can find tiny, nearly transparent sea slugs
with a pair of appendages in the shape of wings.
As far as slugs go, these so-called sea angels are pretty adorable.
But they’re also pretty ferocious predators.
They’ve evolved that way because for as long as they’ve been around,
they’ve been in an evolutionary arms race with their main prey: the sea butterfly.
And by exploring just how these angelic-looking slugs conquer their prey,
we can uncover the fascinating adaptations this species has developed to survive.
Now, it can be a little hard to imagine
these creatures as terrifying predators because,
aside from the angel wings, they’re not exactly huge.
Like, the biggest ones are around 7 centimeters long,
and many measure less than 2 centimeters.
Plus, aside from the wings, they basically look like regular land slugs.
They’re technically pteropods,
a group that falls under the same taxonomic umbrella as land snails and slugs.
But out in the ocean, far from being the slow, innocuous garden pests we know, s
ea angels are ruthless hunters.
They feed on other swimming snails, including the sea butterfly,
a close relative of theirs that lives in a shell.
And thanks to some incredible adaptations,
sea angels have become experts at hunting down and devouring their prey.
One advantage the sea angels have is that despite being slugs,
there’s nothing snail-paced about them.
They can zip through the water at 10 centimeters per second,
almost as fast as a goldfish! Which is enough to easily outpace their prey.
Sea butterflies’ top speed is less than half as fast.
Sea angels get this speed from their wings, which act like oars on a boat,
propelling them straight through the water with up to three strokes a second.
Oddly enough, their wings have evolved to be smaller than their relatives’,
but thanks to their swimming technique, sea angels are still faster.
They’re not always zooming around, but they’re capable of bursts of speed when they need it.
But sea angels don’t just rely on speed to capture their prey.
Sometimes they do the opposite of chase: They just wait.
For instance, one species of sea angel has basically figured out
how to be the world’s laziest predator. It literally gets its prey to reel it in.
The reason it works is because this sea angel preys on a type of sea butterfly
that feeds with the help of a mucus web.
It’s roughly the same concept as a spider web, except, instead of silk,
it’s made of mucus that the sea butterfly expels from its foot.
Which, yes, a sea butterfly has feet! Or, well, foot, singular.
They’re really just modified swimming appendages.
Anyway, normally, sea butterflies use this web to catch
plankton and other floating particles.
Then, when it’s mealtime, they pull the web back in and eat the food they’ve caught.
Except… sometimes they end up reeling in something that wants to eat them.
Because now and then, a hungry sea angel attaches itself to one of these webs.
Then, when the sea butterfly pulls it in, the tables turn,
and the sea angel eats the sea butterfly.
Among other animal species,
hunting is often an extremely expensive part of a predator’s energy budget.
But this passive hunting technique is a remarkable adaptation
that lets this species of sea angel conserve energy while keeping itself well fed.
Whether a sea angel chases down its meal
or has itself delivered straight to its prey, it wastes no time digging in.
And it essentially uses built-in silverware stored in the top of its head to eat efficiently.
It can’t just devour the sea butterfly whole because it’s in a shell.
So the sea angel opens its mouth and extends a set of terrifying-looking tentacles
called buccal cones to scoop the sea butterfly out.
These tentacles are tricked out with hooks, barbs…
Some even have suction cups like octopus tentacles.
So, the sea angel reaches these into the opening of the shell
and uses the hooks on them to yank tissue from the sea butterfly toward its mouth.
With its mouth, it holds onto that tissue
while its tentacles reach back into the shell to grab more of the sea butterfly,
until the whole thing is out of the shell and ready to eat.
This process is so fast that sometimes,
the sea angel devours its whole meal in just two minutes.
There’s no other creature that hunts and eats quite like the sea angel.
And one important reason why these whimsical-looking
creatures developed such specific
and ferocious hunting tactics is because they eat an incredibly specific diet.
Some species eat only sea butterflies.
So, as sea butterflies evolved to outsmart sea angels,
sea angels evolved further to keep up with their prey.
The two have basically been playing evolutionary chess forever.
And it shows us just how many evolutionary moves a species is capable of
when it meets its match.
MBA Outro: Thanks for watching this episode of SciShow,
which was a collab with Monterey Bay Aquarium!
They worked together on an exhibition,
“Into The Deep: Exploring Our Undiscovered Ocean,” to give visitors to the Aquarium a rare look
at some of the animals that thrive in the least-explored area of the planet, the deep sea!
So go check out our fronds at the Aquarium!
Their YouTube channel has awesome videos about the deep sea,
and on the Aquarium’s website,
you can make a donation to support their exhibits, education programs,
and ocean conservation work.
[ outro ]