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 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.
