Most complex organisms have a permanent hole for excreting waste. (Though there are exceptions, like the warty comb jelly, which forms an anus only when nature calls.) In bipeds and quadrupeds, the general vicinity of this orifice is fairly obvious. That isn’t the case with the eight-armed octopus. You may already know that the cephalopods can change colors and squeeze through tight spaces, but how do they expel waste?
According to the Monterey Bay Aquarium, octopuses poop from their siphon or funnel, a large, tube-like structure they also use to shoot water. It’s located on the side of the octopus‘ mantle, which is the large sac above its eyes.

Surprisingly, though, the mantle doesn’t contain its brain (which is actually looped around its esophagus like a donut.) Instead, it holds organs like the animal’s three hearts, gills, and digestive system. The octopus’ digestive tract is pretty alien compared to ours. The Marine Detective explains that when an octopus’ meal is fully digested, it travels out of the stomach and through the intestine until it reaches the end of the organ, which is located at the beginning of the siphon. Since the intestine is funnel-shaped, the excrement comes out in the form of a string. The color of octopus feces depends on its diet. Cephalopods that eat more bivalves, such as scallops, are more likely to have white poop, whereas octopuses that feast on red crabs tend to excrete red feces.
The siphon isn’t only good for releasing waste. Octopuses can use it to squirt ink at predators and make a great escape [PDF]. It’s also a powerful steering tool. Octopuses use the siphon to propel themselves forward by sucking water into their mantle cavities and quickly pushing it out through the tube. The backward force of the water allows the octopus to pick up incredible speed. When the animal moves the siphon, the octopus can change its direction, too. Other cephalopods like squids and cuttlefish also use funnels for jet propulsion.
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