Where Are an Octopus's Testicles? Not Where You Think

If you've heard that an octopus keeps its testicles in its head, you've been bamboozled by one of the internet's favorite animal anatomy myths. The truth? Male octopuses have a single testis located in the mantle—the bulbous body sac that houses most of their organs—not anywhere near their head.

Where Everything Actually Is

Octopus anatomy is genuinely bizarre, which is probably why this myth gained traction. Unlike humans, who keep their reproductive organs in a predictable spot, octopuses pack almost everything into their mantle cavity. The testis sits snugly inside this sac alongside the digestive system, gills, and other vital organs.

The complete male reproductive system is surprisingly complex: the testis connects to a vas deferens, which leads to a spermatophoric gland system (essentially a seminal vesicle and prostate), then to Needham's sac where sperm packets are stored, and finally to a terminal duct. All of this plumbing is internal, enclosed in what scientists call the "genital bag."

So Where's the Head?

Here's where it gets confusing: an octopus's "head" is actually the area between its eyes, and what looks like a head to us is often the mantle. The eight arms sprout directly from around the mouth, which sits at the center of the arm crown. The mantle is behind and above this area.

People see that bulbous mantle and assume it's the head. It's not. It's more like a body sac. But since the mantle is close to what we'd consider the "head region," the wires get crossed, and suddenly you've got a viral fact claiming testicles are in the head.

Why This Myth Won't Die

The octopus testicle myth persists because cephalopod anatomy genuinely doesn't map onto anything we're familiar with. These are animals with three hearts, blue blood, and a beak where you'd expect a butthole. Their entire body plan is alien compared to vertebrates.

Add in the fact that octopuses have no bones (except that beak), can squeeze through impossibly small spaces, and can change color in milliseconds, and you've got an animal that seems to break all the rules. When everything about an octopus is weird, one more weird fact doesn't get questioned.

The real fascinating part? Male octopuses use a specialized arm called a hectocotylus to transfer sperm packets to females. One arm literally becomes a reproductive organ. That's the actual weird genital fact worth knowing.

So next time someone tells you octopus testicles are in their head, you can set the record straight: they're in the mantle, exactly where you'd expect vital organs to be—if you expected anything about octopus anatomy to make sense.