A surprisingly engaging – and informative – article on the evolution of the… well, you’ll get the picture.
“One unusually aerated specimen, a type of polyclad flatworm, sports multiple anuses that speckle its backside like feces-spewing freckles. Two others, a pair of sponge parasites called Syllis ramosa and Ramisyllis multicaudata, will twine their body through host tissues like a tapestry of tree roots, with each tip terminating in its own proprietary butthole; they have hundreds, perhaps thousands, in total. (It’s not totally clear why these animals and others spawned an embarrassment of anuses, but in at least some cases, Hejnol thinks it’s a logical outcome of a branched digestive system, which can more easily transport nutrients to a body’s every nook and cranny.)”