Like many of its kind, the giant California sea cucumber Parastichopus californicus is an anal ventilator' - it pumps sea water rhythmically in and out of its rear end to aerate finely branched structures in its large intestine called respiratory trees, which absorb oxygen from the water.
What sets P. californicus apart from the rest is that it doesn't just breathe through its anus -it eats through it, too. The respiratory trees also serve as filters, sieving algae and other microbes suspended in the water for digestion in the usual manner.
Meanwhile, up at the front, the cucumber's oral tentacles rummage around for morsels in the sediment. With a mouth at each end, the creature is able to exploit two different food sources simultaneously.
Many other animals, including featherstars and some worms and crustaceans, are also known to anally ventilate, so the behaviour might yet turn out to be a rather common one.
Definitely worthy of a place on our weirdest sea creatures list if not weirdest animals
Meet another weird sea cucumber that fires poisonous intestines from its butt to deter predators. Don't worry, they grow back...