Butt munchers

miscukeSome animals vent their anuses.  And, no, I’m not referring to the act of waving a hand around ones posterior to diffuse the gaseous remnants of chilidogs.   Some sea stars, sea cucumbers, crinoids, worms, and crustaceans all pump huge volumes of water into and out of their anus.

Why would you do this outside of ensuring a clean derriere?

Moving large volumes of water across the anus, like a biological bidet, might help with excretion, but it could also be used for respiration.  Think of all that surface area available to diffuse oxygen out of the water into the body!  Or the anus could even be used for feeding…

Wait, what?

In the words of a newly published study (honest to god this is the very first line of the paper),

“An animal is not expected to ingest food through its anus.”

In adult sea cucumbers the cloaca (a cavity already doing double duty for the release of excrement and genital products) rhythmically pumps huge amounts of water in and out. It is already known that this pumping brings oxygen rich water across a highly branched respiratory tree.  Thus the cloaca is now pulling a function trifecta.  But what about quadfecta?


William Jaeckle and Richard Strathmann placed Parastichopus californicus, a beast of sea cucumber lending to its common name the Giant California Sea Cucumber, in aquarium with a single celled algae labeled with a radioactive isotope of carbon.  At several time intervals Jaeckle and Strathmann looked inside the sea cucumbers to see where the radioactive carbon went.  They also repeated this with some larger iron-labeled molecules.

Screen Shot 2013-03-06 at 7.44.31 PM

Blue spots from iron stained molecules can be seen in the tissue of the respiratory tree

After some time the respiratory tree, that only receives outside water through the anus, was resplendent with iron and radioactive carbon.  In other words, food passed through the anus and was taken up the respiratory organs.  The highest concentrations were found in a unique organ called he rete mirabile that serves as a go-between for the respiratory tree and gut.

So, yes, sea cucumbers can eat through their anuses. The authors refer to this more scientifically as “bipolar feeding.” The authors do note that the amount of food taken in through the anus is likely to be small, given that the…ahem…exchange of water is only likely to be about ¼ to 4 cups of water an hour.

William. B. Jaeckle and Richard. R. Strathmann The anus as a second mouth: anal suspension feeding by an oral deposit-feeding sea cucumber Invertebrate Biology 132.  Article first published online: 29 JAN 2013 | DOI: 10.1111/ivb.12009

UPDATE: I see Echinoblog has beaten me to the punch on this one.

Dr. M (1729 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, a National Science Foundation supported initiative. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (http://deepseanews.com/), a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web. His forthcoming book, Science of the South (http://www.scienceofthesouth.com/), connects cultural icons of South such as pecan pie with the science behind them.

8 comments on “Butt munchers
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  3. Some sea stars, sea cucumbers, crinoids, worms, and crustaceans all pump huge volumes of water into and out of their anus.

    Some turtles too (not the deep seas kind).

  4. Pingback: Sea cucumbers, stars and urchins on Lord Howe | A-roving I will go

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