This sea creature breathes through its butt - Cella Wright

Can you guess what you’re looking at?

Is it a fuzzy sock? An overripe banana?
A moldy tube of toothpaste?

In fact, this is the humble sea cucumber,
and while it might look odd,

its daily toil paves the way for entire
ecosystems to thrive.

Sea cucumbers are members of the phylum
Echinodermata,

along with sea urchins, starfish and
other radially symmetrical,

“spiny-skinned” marine invertebrates.

Some sea cucumbers have feathery tentacles
flowing from their mouths,

some are puffed like bloated balloons,
and others simply look like Headless Chicken Monsters –

the actual name given to a rare
deep-sea species.

But they are generally characterized
by their long, cylindrical shape.

A sea cucumber is essentially a brainless,
fleshy form surrounding a digestive tract,

bookended by a mouth and an anus.

Adhesive tube feet run the
length of their bodies

and allow them to scoot along
the seafloor.

Specialized tube feet can be used
for feeding and respiration,

though many sea cucumbers actually
breathe through their anuses.

Rhythmically contracting and relaxing
their muscles,

they draw water in and out over an
internal lung-like structure

called a respiratory tree
that extracts oxygen from seawater.

Certain species of crabs and pearlfish

take advantage of this
rhythmic action and,

once the sea cucumber’s anus is dilated,
they shimmy in and take shelter.

The rear end of a single sea cucumber can
harbor up to fifteen pearlfish at a time.

However, it seems that not all sea
cucumbers

put up with this intrusive behavior.

Some species are equipped with five teeth
around their anus,

suggesting that they may have taken

an evolutionary stand against
unwanted guests.

But even sea cucumbers that lack anal
teeth

are outfitted with tools to
defend themselves.

They evade threats and launch
counter-attacks

using their mutable collagenous
tissue, or MCT.

This gel-like tissue contains bundles of
collagen, called “fibrils.”

Proteins can interact with these fibrils
to slide them together,

stiffening the tissue, or apart,
softening it.

This versatile tissue has many advantages:

it aids in efficient locomotion, enables
sea cucumbers to fit into small spaces,

and allows them to reproduce
asexually by splitting apart.

But MCT’s most explosive application
is employed when a predator attacks.

By loosening the attachments of internal
tissues

then quickly softening and
contracting their muscles,

many species are capable of shooting
a wide range of organs out of their anuses.

This act is called “evisceration”

and it’s a surprisingly effective
defense mechanism.

In addition to startling and
distracting predators,

the innards of some sea cucumber
species are sticky and toxic.

Evisceration may seem drastic,

but sea cucumbers are able to regenerate
what they’ve lost to their gut reaction

in just a few weeks’ time.

Aside from the few species that have
evolved to swim

and those that feed without moving,

many of these cumbersome creatures
pass their time grazing the seabed.

Sea cucumbers are found everywhere from
shallow shores

to abyssal trenches 6,000 meters
below sea level.

On the deep sea floor, they comprise the
majority of animal biomass,

reaching up to 95% in some areas.

As these sausage-shaped wonders trudge
along, they vacuum up sand,

digest the organic matter it contains,
and excrete the byproduct.

In this process, sea cucumbers clean
and oxygenate the seafloor

by breaking down detritus and recycling
nutrients.

This creates the conditions for sea grass
beds and shellfish to thrive.

Sea cucumber excretions can also aid in
coral formation

and may play a role in buffering marine
environments from ocean acidification.

As the ocean’s vacuum cleaners, they
are very good at their job:

about half of the sandy seafloor

is thought to have passed through the
digestive tract of a sea cucumber.

So, the next time you’re
rejoicing in the feeling

of sand crunching between your toes,
consider this:

those very grains of sand might have,
at one point or another,

been excreted by a pickle that breathes
through its butt.