IT LIKES a blowout, in more ways than one. When attacked, the giant California sea cucumber (Parastichopus californicus) has an explosive escape strategy: it squirts its digestive system out of its anus in a sticky mess to confuse its foe. That's all well and good, but surely it can't survive without its guts? Not true: to get by, it eats through its anus.
The sea cucumber's anatomy is a little peculiar. Its respiratory system is connected to its anus, through which it sucks water to take in dissolved oxygen. When Richard Strathmann of the University of Washington in Friday Harbor added algae containing radioactive carbon-14 to the creature's environment, he found that carbon-14 ended up in the respiratory system. That suggests the sea cucumber can take in algae through its anus as well as its mouth (Invertebrate Biology, doi.org/kcm).
It's not clear how the respiratory system digests the algae, or why anal feeding evolved. Strathmann says it could have begun as a way to pick up extra food from the surrounding water. "Nutrition through the anus is a remarkable reversal of what we expect," he says.
This article appeared in print under the headline "Meet the ultimate bottom feeder"
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