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  • 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-skinnedmarine 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, calledfibrils.”

  • 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 calledeviscerationand 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 seafloor, 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.

Can you guess what you're looking at?

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This sea creature breathes through its butt - Cella Wright

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    王杰   に公開 2020 年 05 月 18 日
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