Changing Planet

Giant Sea Cucumber Eats With Its Anus

Most kindergarteners can tell you that an animal eats with its mouth, not its butt.

One species of sea cucumber, however, didn’t appear to get the memo: Scientists have discovered that the giant California sea cucumber (Parastichopus californicus) actually uses its anus as a second mouth.

A giant sea cucumber in the Pacific Ocean. Photograph by Gerald and Buff Corsi, Visuals Unlimited


Scientists already knew that the marine invertebrate, which lives in the shallow ocean waters off the Pacific coast of North America, breathes with its butt.

Because they don’t have lungs, sea cucumbers rely on respiratory trees, a set of long tubes running down either side of the body with a lot of different branches. P. californicus is shaped like a hollow tube, with a mouth at one end and its anus at the other.

The respiratory trees receive oxygen when water is pumped through their anus using the muscles of their cloaca, an opening at the end of the intestinal tract. (Watch a video of sea cucumbers fighting with their guts—literally.)

The 20-inch-long (50-centimeter-long) animal is no slouch: It can pump 3.5 to 4 cups of water per hour through its anus, transferring the oxygen from the water into its respiratory trees, which then oxygenates its cells.

sea cucumber picture
A diver holds a sea cucumber off Ft. Lauderdale, Florida. Photograph by Lois Booth, My Shot


The sheer amount of water flowing into the anus got two invertebrate biologists thinking—since P. californicus sifts plankton and other small particles from water using its tentacles, could it do something similar using its anus?

Though “an animal is not expected to ingest food through its anus”—as William Jaeckle and Richard Strathmann note at the beginning of their study in the March issue of Invertebrate Biologyit turns out the answer is yes.

Multipurpose Anus

Their first hint that the sea cucumber anus was doing triple duty came from a structure called the rete mirabile, a set of blood vessels that connect the sea cucumber’s respiratory trees with its gut.

Initially, Jaeckle, of Illinois Wesleyan University, and Strathmann, of the University of Washington, thought that the rete mirabile was used to transfer oxygen from the respiratory trees to the gut. But if P. californicus were obtaining food via its anus, it would likely use the rete mirabile to transfer the food to the gut. (Watch a video of a hairy sea cucumber.)

sea cucumber picture
A sea cucumber in Okinawa, Japan. Photograph by Gary Hughes, Your Shot


To test their idea, the team fed several sea cucumbers radioactive algae, which also contained iron particles. The iron and radioactivity proved an easy way to trace the food as it traveled through the sea cucumber’s body. For instance, areas of the body with the highest concentrations of radioactivity would provide clues about which orifices the animal was using to eat.

Not surprisingly, the results showed that the sea cucumbers ate the algae through their actual mouths, which then traveled through their gut. (See pictures of colorful sea creatures.)

However, the researchers also found a high level of radioactivity when they looked at the rete mirabile. The only way that those blood vessels could have such a high concentration of radioactivity is if the animal was transferring food from the respiratory trees to the gut via the rete mirabile.

Bottom Feeders

When the scientists looked at tissue samples from the sea cucumber under the microscope, they found even more hints that P. californicus was using its anus as a second mouth: They found small pieces of algae and iron in the respiratory trees near the anus.  (Also see “Why Sea Slugs Dispose of Their Own Penises.”)

In addition, the sea cucumber’s respiratory trees had small, finger-like projections known as microvilli that are normally found in the gut and aid with nutrient absorption. This also indicated that P. californicus was absorbing food using its anus and respiratory trees.

The authors conclude that although they looked only for evidence of bipolar feeding—the more formal and perhaps polite term for eating with your butt—in one species of sea cucumber, many other species are likely to use this method of feeding.

Bottom line? Eating with your butt may not be all that unusual.

Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at
  • Issahaku yakubu

    Nageo is really educating some of us who wants to know more of the natural world. Infact life is full of wonders n signs which shows more are yet to be disvovered.

  • Richard

    It’s South Park come to life! If they can poop w/their mouth, the parallels are complete.

  • Ima Ryma

    Giant sea cucumber am I,
    Look like the veggie, but marine
    Animal – either gal or guy.
    Now this may sound a bit obscene,
    My anus is a second mouth,
    So bipolar feeding can be
    On either end – the north or south,
    Depending on where are algae.
    Humans, while ever butting in,
    Noticed this special trait of mine,
    Gave me tests again and again,
    Kind of like going out to dine.

    Butt use for head stuff’s not so rare.
    Humans often talk out of there.

  • Dewey Cheatem

    If it could only talk out it’s butt, the sea cucumber would be a natural in Congress!

  • Mike

    Cartman was right

  • Hugh Janus

    Sea Cucumbers are the most disgusting of all animals, they eat, breath, sh*t and f**k all through the same hole. When they are threatened they turn themselves inside out and spray purple stained intestines on their attacker. So Cool!

  • marc

    Take THAT Platypus!

  • Richard

    Why show a picture of someone handling a sea cucumber ? It sends out a bad message to others – that this is acceptable behaviour. Poor and unresponsible journalism…

  • Mititelu Dumitru

    Life is full of miracles which are still found.
    Nageo is for some of us who want to know more of the natural world.

  • that guy

    Like this?

  • C. Cucumber
  • a.p.datingaling,water…..the precious gifts that our God gave to us..those are wonderful and beautiful and totally fascinating..

  • Diane Feinstein

    Hey that’s my cousin!

  • Nott Ingham

    Humans have a surprising number of two-way holes as well.

  • sami Zahringer

    My 10-year-old daughter is going to LOVE this.

  • nanang

    how the poop ? in Indonesia sea cucumber is export commodity to HKG and others asia country its quite profitable

  • Joseph Morse

    Giving new meaning to the term “bottom feeder”.

  • Carole-Anne Pardoe


  • MAX


  • joro

    first time i see!!

  • Runner4703

    Kind of reminds me of Jenna Jamison.

  • junejo a jalil

    really this is large marine echinoderms and big sea cucumber only found in oceans.

  • S.R.Krishnarajah

    see this nice article

  • John Ngatia Kupuny

    What a wonderful thing, new discoveries are informing us about our earth. Thanks NATGEO.

  • Katie

    I see you switched out the Florida diver/cucumber pic for an actual photo of a P. californicus, which should have been super easy to find in the first place. Now the Florida species is up on Failblog’s School of Fail representing your article. I expect better, Nat Geo!

  • bottomfeeder

    Another name for bottom feeder, you are eating out of your butt. Your butt!!

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