An octopus can regrow its arms with cells. It takes about 130 days for new limbs to fully grow out. Octopuses need their limbs for movement, grasping, and feeling, which is why it’s so important that they stay intact.
Octopuses have eight long arms full of suckers. These are unique to the octopus, as no other animal has this anatomy.
These arms are incredibly important to the octopus, which is why they have evolved with a crucial ability: to regrow their arms. But how does this work?
This article aims to shed a light on the process of octopus limb regeneration and answer all questions on how octopus arms grow back.
Do Octopus Arms Grow Back?
Octopus arms grow back in about 130 days after they get severed. It takes two to three days before the new limb is noticeable. They regenerate their arms via epithelial (cells on the surface of the skin, blood vessels, and organs) and stem cells.
Octopuses do not get scars when their arms are severed. Instead, the wound gets covered by a layer of cells called the epithelium. Under the epithelial layer, blastema forms (a mass of undifferentiated cells). Undifferentiated cells are cells that have not yet developed to be specialized cells (like blood cells or epithelial cells).
Over time, this blastema gets pushed out due to cell division and suckers start to appear on the knob-like appendage. It takes two weeks for stem cells and blood vessels to arrive. The arm is not yet functional at this point.
The new, fully-functioning arm is formed in about 130 days.
How Many Arms Do Octopuses Have?
Octopuses have eight limbs. There are two types: arms and legs. Octopuses have six arms and two legs.
The name octopus refers to the number of their limbs. Octopus derives from the ancient greek words “okto”, meaning eight, and “pus”, meaning feet.
Not all limbs of the octopus are multi-functional. There are two types of limbs with different usages:
1. Octopus Arms
Octopuses have three pairs of arms. All of their limbs are arms, except the back two.
Octopuses are generally ambidextrous, but most prefer to grab food with their third arm from the front.
Males have one arm called a hectocotylus. It transfers spermatophores to females. The male can use it in two ways during mating: as other animals use the penis or detach it in a process called autotomy.
Here are some activities for which octopuses use their arms:
2. Octopus Legs
Octopuses have one pair of legs. These are the two back limbs. Octopuses do not use these for grabbing and they generally get around on the seafloor with them.
Here are some ways in which octopuses use their legs:
- Pushing off the seafloor
What Do Octopus Arms Look Like?
Octopus arms are long appendages starting at the bottom of the head. They are muscular limbs that are wide at the base and narrow near the tip. The underside of each arm is covered with suckers.
Octopus arms are muscular appendages without bones, as octopuses are invertebrates. They have small webbings between the arms, but this is more prominent in some species (such as the umbrella octopus).
The beak (the mouth of the octopus) is located at the base of the arms.
|Number||Eight (six arms, two legs)|
|Location||Starts at the bottom of the head|
|Shape||Wide at the base, gradually narrower nearing the tip, webbing between the arms|
|Skin and Muscles||Covered with delicate, color-changing skin. Arms are pure muscles without bones.|
|Suckers||Usually two rows of cup-like knobs on the bottom side of each arm|
How Do Octopus Arms Regenerate?
Octopus arms regenerate via a series of cell reactions. The wound is first covered by an epithelial layer, whereafter undifferentiated cells form underneath that specialize into needed cells later. After a few weeks, stem cells and blood vessels pour in. It takes about 130 days to grow a fully-functional arm.
The regeneration of octopus arms is lizard-like. The differences are that lizards regrow their limbs twice as fast as octopuses. In turn, regrown octopus arms are sturdier and more like the original than regrown lizard limbs.
Octopuses’ ability to regenerate their arms in such detail is heavily debated. Studies suggest that a protein called AChE may play an important part in the regeneration process.
This protein becomes active in damaged arms after three weeks and quiets down on day 42. Between days 21 and 42 is the period when new suckers and chromatophores appear on the growing arm.
The wound goes through a series of drastic changes before it grows back. Here is the process of arm regeneration in detail:
- Arm is severed.
- The wound gets covered by the epithelium, a layer of cells.
- A mass of undifferentiated cells called blastema accumulates under the epithelium.
- A knob forms on the wound.
- The blastema pushes the epithelium outwards through cell division.
- A hook-like shape forms.
- Blood vessels and stem cells pour in.
- Suckers and chromatophores start forming.
- Gradual growing until the arm is fully regrown.
How Long Does It Take for an Arm to Grow Back?
It takes about 130 days for an octopus arm to regenerate. The knob-like growth turns into a hook-like structure within three days. A common octopus’ arm severed at its base grows about 0.3 inches a day.
After about two weeks, stem cells and blood vessels start to pour into the appendage. This is when suckers and chromatophores (color-changing cells in the skin) appear.
From this point until the process finishes, the arm grows steadily to its full extent.
Octopus Arm Size Table
Each octopus species has vastly different arm lengths. The smallest star-sucking pygmy octopus’ arms are less than an inch long, whereas giant Pacific octopuses have arms up to 14 feet long.
An individual octopus has eight different-sized arms. However, there aren’t any regular patterns as to which arms are longer and the difference is insignificant.
|Giant Pacific Octopus||14 feet arm span|
|Common Octopus||3.3 feet|
|California Two-Spot Octopus||23 inches|
|Caribbean Reef Octopus||30 in|
|Atlantic Pygmy Octopus||3.5 inches|
|Mimic Octopus||1.5 feet|
|Star-Sucking Pygmy Octopus||Less than an inch|
Octopuses grow their arms back. It takes 130 days for an arm to fully regenerate. The main components of regrowth are the epithelium, the blastema, stem cells, and blood vessels. The arms grow back at a rapid pace and an arm span can be 14 feet long.
Octopuses have eight arms. The two back arms are used for crawling and pushing off the seabed, while the other six are for grabbing, swimming, and feeding. Male octopuses use one of their arms to impregnate females.
Are Tentacles and Arms the Same?
No, tentacles and arms aren’t the same. Although tentacle is often used to refer to all cephalopod limbs, they are scientifically distinct from arms. Arms have suckers along most of their length, while tentacles only have them on their tips. Octopuses, therefore, have arms.
Do Octopuses Eat Their Own Arms?
Yes, octopuses sometimes eat their own arms. Octopuses may eat their own arms for a variety of reasons. Bored octopuses confined to small spaces engage in autophagy. Octopuses that have mated enter a state called senescence, during which females tear bits out of their arms.
Do Octopus Arms Have Brains?
Yes, octopus arms technically have separate brains. Octopuses have a central brain, but the majority of their neurons (acting as mini-brains) are located in their arms. Octopus arms remain responsive for several hours after being separated from the body.