WEBVTT

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Can you guess what you’re looking at?

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

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

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

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Sea cucumbers are members 
of the phylum Echinodermata,

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along with sea urchins, starfish 
and other radially symmetrical,

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“spiny-skinned” marine invertebrates.

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Some sea cucumbers have feathery tentacles
flowing from their mouths,

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some are puffed like bloated balloons,

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and others simply look like 
Headless Chicken Monsters—

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

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

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

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bookended by a mouth and an anus.

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Adhesive tube feet 
run the length of their bodies

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and allow them to scoot along 
the seafloor.

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Specialized tube feet can be used 
for feeding and respiration,

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though many sea cucumbers actually 
breathe through their anuses.

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Rhythmically contracting and relaxing 
their muscles,

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

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called a respiratory tree
that extracts oxygen from seawater.

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Certain species of crabs and pearlfish

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take advantage of this 
rhythmic action and,

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

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

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However, it seems that not all 
sea cucumbers

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put up with this intrusive behavior.

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Some species are equipped with five teeth
around their anus,

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suggesting that they may have taken
an evolutionary stand

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against unwanted guests.

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But even sea cucumbers 
that lack anal teeth

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are outfitted with tools 
to defend themselves.

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They evade threats 
and launch counter-attacks

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using their mutable collagenous tissue, 
or MCT.

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

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Proteins can interact with these fibrils 
to slide them together,

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stiffening the tissue, or apart, 
softening it.

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This versatile tissue has many advantages:

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it aids in efficient locomotion,

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enables sea cucumbers 
to fit into small spaces,

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and allows them to reproduce 
asexually by splitting apart.

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

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By loosening the attachments 
of internal tissues

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then quickly softening 
and contracting their muscles,

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many species are capable of shooting 
a wide range of organs

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out of their anuses.

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This act is called “evisceration”

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and it’s a surprisingly effective 
defense mechanism.

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In addition to startling 
and distracting predators,

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

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Evisceration may seem drastic,

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

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in just a few weeks’ time.

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Aside from the few species 
that have evolved to swim

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and those that feed without moving,

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

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Sea cucumbers are found everywhere 
from shallow shores

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to abyssal trenches 6,000 meters 
below sea level.

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

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reaching up to 95% in some areas.

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

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

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In this process, sea cucumbers clean 
and oxygenate the seafloor

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by breaking down detritus 
and recycling nutrients.

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

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Sea cucumber excretions can also aid 
in coral formation

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

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

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about half of the sandy seafloor

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

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So next time you’re rejoicing 
in the feeling of sand

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crunching between your toes, 
consider this:

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

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been excreted by a pickle 
that breathes through its butt.