Does an Octopus Have Arms or Tentacles? Eight Arms Explained

Arms vs tentacles: what is the difference?

All cephalopods, the group that includes octopuses, squid, cuttlefish and nautiluses, have a ring of limbs around the mouth. Scientists sort these limbs into two kinds.

Arms are relatively short, thick and muscular, with suckers along most or all of their length. They are used for crawling, holding prey, handling objects and, in males, mating.

Tentacles in squid and cuttlefish are a single specialized pair, longer and thinner than the arms, with a bare stalk and a widened tip called the club, where the suckers or hooks are concentrated. They work like a harpoon: the squid shoots them out in a split second to snatch a fish or shrimp, then passes the catch to its arms. In the giant squid, the two feeding tentacles can be about twice as long as the body and arms combined.

So the common phrase “octopus tentacles” is a scientific slip. An octopus has eight arms, and none of them is a tentacle.

Which cephalopods have tentacles?

The chambered nautilus is the odd one out. Instead of arms, it has dozens of slender, sucker-less tentacles with ridged, sticky surfaces, which it uses to grip food. For the other differences between the eight-armed and ten-limbed groups, see octopus vs squid.

What octopus arms are made of

An octopus arm has no bones or joints. It is a muscular hydrostat, the same design as the human tongue or an elephant’s trunk: layers of muscle running lengthwise, across and around the arm press against each other, so the arm can bend anywhere, twist, stretch out, shorten or turn stiff.

In the common octopus, each arm carries two rows of suckers. A sucker has an outer rim that seals against a surface and an inner cup whose muscles change the pressure, producing a strong grip. Each sucker can move and grip independently.

Scientists label the arms L1 to L4 and R1 to R4, from front to back. The front arms tend to be used more for reaching and exploring, and the back arms for crawling and pushing off. In males of the genus Octopus, the third right arm is a hectocotylus, with a spoon-shaped tip for passing sperm to the female.

When a common octopus brings food to its mouth, studies have found that it bends the arm at two points, creating temporary “joints” that work like an elbow and a wrist. It builds a jointed limb out of a boneless one whenever it needs one.

Arms that taste and think

Octopus arms are not just limbs; they are sense organs and partly independent decision makers. About two-thirds of an octopus’s neurons lie in the nerve cords of its arms, and each sucker has its own small cluster of nerve cells.

The suckers are covered in chemical sensors. A 2020 study on the California two-spot octopus identified special receptor proteins in the suckers that let them taste the surfaces they touch. An octopus can probe a crack it cannot see into and “taste” whether a crab is inside.

Arms also avoid tangling with each other. A 2014 study found that a chemical in octopus skin stops the suckers from sticking to the octopus’s own body, although the animal can override this when it wants to. There is even evidence that octopus arms respond to light, so an arm can tell whether it is exposed. This distributed nervous system is a key part of how smart octopuses are.

Can an octopus regrow an arm?

Yes. Octopuses often lose arms to predators such as eels and fish, and a lost arm grows back fully, with muscles, nerves, suckers and color-changing cells. The wound closes quickly, a small pale tip appears, and the new arm lengthens over the following weeks to months, depending on the species, the size of the injury and the water temperature.

Some octopus species can even shed an arm on purpose to escape a predator, much as some lizards drop their tails. Occasionally regrowth goes wrong and an arm forks into two or more tips. Regeneration is common in invertebrates; for another famous example, see can starfish regrow their arms?

Why do people call them tentacles?

In everyday English, a tentacle is any long, flexible limb used for feeling or grasping, which is why jellyfish, sea anemones and snails are said to have tentacles, and why the word stuck to octopuses. Dictionaries accept this broad meaning, so calling octopus arms tentacles in casual conversation is not really wrong.

In biology, though, the distinction matters, because it reflects real differences in anatomy and evolution. Squid, cuttlefish and octopuses all descend from ancestors with ten limbs. Squid and cuttlefish turned one pair into specialized tentacles, while the octopus lineage lost one pair of limbs altogether. So the correct answer to the question is simple: eight arms, zero tentacles.