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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, its daily toil paves the way for entire ecosystems to thrive.
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Sea cucumbers are members of the 'phylum Echinodermata,' along with sea urchins, starfish and other radially symmetrical, “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: 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, bookended by a mouth and an anus.
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Adhesive tube feet run the length of their bodies and allow them to scoot along the seafloor.
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Specialized tube feet can be used for feeding and respiration, though many sea cucumbers actually breathe through their anuses.
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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.
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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.
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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 put up with this intrusive behavior.
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Some species are equipped with five teeth around their anus, suggesting that they may have taken an evolutionary stand against unwanted guests.
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But even sea cucumbers that lack anal teeth are outfitted with tools to defend themselves.
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They evade threats and launch counter-attacks 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, 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 then quickly softening and contracting their muscles, many species are capable of shooting a wide range of organs out of their anuses.
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This act is called “evisceration” and it's a surprisingly effective defense mechanism.
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In addition to startling and distracting predators, the innards of some sea cucumber species are sticky and toxic.
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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.
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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.
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Sea cucumbers are found everywhere from shallow shores to abyssal trenches 6,000 meters below sea level.
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On the deep seafloor, they comprise the majority of animal biomass, reaching up to 95% in some areas.
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As these sausage-shaped wonders trudge along, they vacuum up sand, digest the organic matter it contains, and excrete the byproduct.
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In this process, sea cucumbers clean and oxygenate the seafloor 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 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: about half of the sandy seafloor 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 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.