[♪ INTRO] All octopuses start out as teeny, tiny plankton, drifting through the ocean at the mercy of
currents. Eventually, though, they get big enough to
settle down and make a home for themselves on the seafloor... but not the blanket octopus. The four species in the genus Tremoctopus
never settle down. Though they get quite big, they spend their
lives wandering the open ocean. And not even scientists know very much about
these nomadic invertebrates. But what they have found out is amazing! It turns out they have some pretty weird traits that help them survive the high seas— including those blanket-like appendages they’re
named after. Most octopuses spend a lot of their lives
hiding, whether it’s in rocky dens, holes in the
sand, or large shells. They only swim around when hunting or defending
their territory —and even then, they’d prefer to crawl. Which I guess makes sense, since they have
no bones to protect their soft, squishy bodies. The only hard part of an octopus is its beak —the calcified mouthparts it uses to eat
its prey. And blanket octopuses are also mostly soft. But still, they don’t seek protection on
the seafloor. They are generally found cruising through
warm, tropical waters around the world. And they can do that because they have all
the usual octopus defenses—like the ability to release
ink and change color at a moment’s notice— as well as a couple of extra tricks. There’s that namesake blanket, for instance. It refers to the long transparent webs of
skin which connect four of a female’s arms. When threatened, she is able to unfurl all
this skin and trail it out behind her like a superhero’s
cape. And in the largest species, she can grow to
be over 2 meters long. So when you combine her size with her incredible
cape, she looks pretty intimidating! If this doesn’t scare off a would-be predator, she may be able to ditch the blanket instead. Lone blankets have been spotted by divers,
and some experts believe that’s because a female can break
it off much like a lizard does its tail when threatened. The idea being that, hopefully, that distracts
the predator long enough for her more essential bits to
escape. And when the animals are smaller, they have another trick they can use. They’re actually immune to the stinging
cells of Portuguese man o’ war and their close
relatives. A young female blanket octopus will swim up
to a man o’ war, rip off its tentacles, and then carry them
around using her suckers. Then, when a threat comes too close, she can
wield them like toxic whips! It’s something the unfortunate scientist
who first published this behavior discovered firsthand. Now the males steal tentacles to defend themselves,
too. But they don’t just wield them when they’re
young because… well… they never get big. In fact, they're so tiny that scientists didn’t
observe them alive until 2002. The males of the largest species only grow
to be about 2.5 centimeters long! On average, males are one one-hundredth the
length and 40 thousand times less massive than their
mates! That’s the most extreme size difference
between sexes that we know of among non-microscopic animals. Just imagine if your spouse were the size
of a walnut. Scientists think that the males evolved to
be so small because all they really need to do is mate. You see, all male octopus have a special appendage called a hectocotylus—what is sometimes
totally seriously referred to as a “sex arm”—that they can fill with
packets of sperm. In most other species, a male sticks this
sex arm into a female’s mantle cavity during courtship to deposit his sperm packets—a process that
can take several hours. But in the open ocean, there’s zero privacy, so romance kind of goes out the window. When a male and female blanket octopus meet, he just rips off his sex arm and quickly sneaks
it into her. The arm crawls on its own up deeper into the
female —where it might find a few other arms already
hanging out. Eventually, the female will run out of space. So for males, it’s not size that matters—it’s
speed. And growing big takes time, so larger males
are at a disadvantage. Once a male has delivered his sex arm, he
dies. His work is done. Then, when the female is ready, she picks
the arm she likes best and squeezes the sperm all over her eggs. If she lived on the bottom like other octopus,
she’d probably lay these eggs in her den so she could care
for them until they hatch. But, since the open ocean lacks adequate housing,
she constructs a cigar-shaped anchor rod for them out of
calcium carbonate —the same stuff in shells and coral skeletons. And around 100 thousand eggs can attach to
this rod, which hangs on one of her arms, keeping them
all safe while she continues to move about the ocean. It’s thought that she dies shortly after
the babies hatch, mostly because that’s what other female
octopus do —but researchers don’t know for sure. In fact, we have a lot left to learn about
blanket octopus, including how they find one another in the
vastness of the ocean, or whether they sleep. In the meantime, we can appreciate these bizarre
animals and the incredible ways they boldly go where other adult octopuses wouldn’t dare. Thank you for watching this episode of SciShow! And a special thank you to our President of
Space, Matthew Brant. Matthew is one of the awesome people that
supports the show through Patreon. So he helps ensure the team here can keep
making free, educational science content. And that, in our completely scientific and
totally unbiased opinion, makes Matthew pretty rad. If you want to learn more about our wonderful
patron community, you can head over to Patreon.com/SciShow [♪ OUTRO]
