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 (1714 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, created to facilitate research to address fundamental questions in evolutionary science. He has conducted deep-sea research for 11 years and published over 40 papers in the area. He has participated in dozens of expeditions taking him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses mainly on marine systems and particularly the biology of body size, biodiversity, and energy flow. He focuses often on deep-sea systems as a natural test of the consequences of energy limitation on biological systems. He is the author and chief editor of Deep-Sea News, a popular deep-sea themed blog, rated the number one ocean blog on the web and winner of numerous awards. Craig’s popular writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.

8 comments on “Butt munchers
  1. Pingback: I’ve got your missing links right here (9 March 2013) – Phenomena: Not Exactly Rocket Science

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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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