Sea cucumbers have a really strange relationship
with their buttholes.
I’m Anna Rothschild, and this is Gross Science.
To begin, let me just clarify that sea cucumbers
don’t exactly have a butt in the human sense.
They have something called a “cloaca”
which is kind of an all-purpose opening.
Lots of animals, including many birds, have
a cloaca, which they use to pee, poop, and
in some cases, mate.
But the sea cucumber takes this whole “all-purpose”
thing a little further.
To begin with, they actually breathe through
their butts.
Rather than using lungs, sea cucumbers take
in oxygen by flushing water over organs called
respiratory trees.
And how does the water get into the sea cucumber?
It’s pumped in through the backdoor by the
muscles of the cloaca.
Sometimes bits of food get pumped in, too.
And at least some sea cucumbers don’t let
those bits go to waste—they can eat with
their butts, as well!
Their respiratory trees possess some intestine-like
properties, and can absorb nutrients.
To be clear, sea cucumbers probably prefer
to eat with their mouths.
But they won’t turn down a tasty morsel
if it happens to float in through the cloaca.
Finally, and perhaps strangest of all, small
skinny fish called pearlfish actually make
sea cucumber butts their home.
Many pearlfish live peacefully with their
sea cucumber hosts.
They’re what’re called “inquilines,”
which means that they’re organisms that
live inside of or in the home of another species,
but don’t hurt it.
However, some species of pearlfish are actually
parasitic and eat the sea cucumber’s reproductive
organs along with other tissue.
Now, sea cucumbers actually have a bunch of
defense mechanisms to avoid predators and
parasites.
One is the ability to expel and regenerate
their internal organs—and for more on that,
see my previous video on the subject.
But they also have chemicals called saponins
in their bodies, including in their Cuvierian
tubules, which are sticky strings that sea
cucumbers shoot out of their cloaca when they’re
attacked.
Saponins usually burst open the cells of the
would-be predator or parasite.
But pearlfish aren’t affected.
And scientists think it might be because they’re
covered in a relatively thick layer of mucus,
which protects them from the toxins.
As a side note, Harlequin crabs, which also
live in and on sea cucumbers, may actually
be attracted to their hosts by those same
chemicals.
Finally, sea cucumbers may have one more defense
mechanism.
Some of them have structures called anal teeth,
possibly to keep the pearlfish out—though,
no one knows for sure if that’s really what
anal teeth are for.
In many species, the fish can slip in anyway.
Long story short, sea cucumbers are really
just gifts to curious people everywhere.
The more I learn, the more I’m impressed
with these guys...and with their butts.
Ew.
