How Many Arms Does a Starfish Have?

Two starfish with different shapes and arms

Have you ever wondered how many arms a starfish actually has? While many of us picture them as having five arms, there’s a lot more to the story.

This article talks about how many arms starfish can have. While many starfish do have five arms, some have more and some have less.

We’ll look at why starfish have different numbers of arms and what makes each kind special. So, continue reading to learn about their amazing arms!

Are Starfish “Arms” Really Arms?

Blue sea stars with five arms

Starfish are often pictured with “arms,” but these are not arms in the traditional sense. Instead, they are extensions of their central body, more accurately described as parts of their head that reach out in all directions.

According to, these arms are equipped with hundreds of hydraulically operated tube feet that serve as multifunctional tools. They allow the starfish to move, eat, and sense their environment.

Each sea star can have up to 15,000 feet on its arms, and all of them are tipped with suction cups.

While it may seem odd to refer to their head extensions as arms, for ease and clarity, we’ll stick with calling them arms in the succeeding sections. 

Fun Fact: With up to 15,000 tube feet attached to their arms, sea stars can propel themselves at speeds of one meter per minute and expertly grab onto their prey.

How Many Arms Does a Starfish Have?

Starfish with five arms isolated in white background

A typical starfish has five arms. But since there are about 1,900 different kinds of starfish, it’s not unusual to see some species with six, seven, or even more than 50 arms! 

For example, the Antarctic sun starfish starts with five but can grow up to 50 arms as it gets older, which they use to catch all sorts of food like krill and small fish.

Interestingly, starfish exhibit other unusual abilities thanks to these many arms. Each arm is equipped with light-sensitive eyespots and suckers capable of detecting chemical signals which can guide them to their next meal. 

Moreover, these versatile limbs also play a crucial role in their reproduction as they contain sexual organs for releasing eggs or sperm into the water.

On my snorkeling trip off the coast of a small island in Bali, I also saw how a starfish, flipped onto its back, skillfully used its arms to turn over. 

Through a coordinated, tripod-like motion, the sea star managed to flip itself back over, which was done with astonishing speed and efficiency. 

Can Starfish Have More Than Five Arms?

Unique starfish with six arms

Yes, starfish can have more than five arms. These extra-armed starfish are not just oddities but are adaptations to their environment.

Having more arms can mean better chances of catching food, moving around, and even hiding from predators.

Consider the Sun Star, specifically the species Pycnopodia helianthoides, which can flaunt up to 24 arms. It uses its many arms to envelop large areas of the ocean floor while searching for prey.

On the flip side, the Crown-of-Thorns Starfish (Acanthaster planci), which has 14 to 21 venomous arms, shows how an abundance of arms can have a less positive impact on the environment.

This sea star’s voracious appetite for coral polyps seriously threatens coral reefs. 

Check out this cool video of a starfish with more than five arms:

Sunflower Seastar: Terrifying Predator? | National Geographic

How Do Starfish Use Their Arms?

Starfish arms do a lot more than just make starfish look like stars. They actually give the starfish some pretty amazing abilities. Here are some of the purposes of the starfish arms:

  • Getting Around: Imagine having suction cups for feet. That’s what it’s like for sea stars. Their arms are covered with tiny tube feet that stick to the ocean floor, helping them crawl around. This is how they explore and find food.
  • Eating: Starfish have a unique way of eating. They can actually push their stomachs out of their bodies right over their food while using their arms to help wrap around and digest it. This lets them eat things much bigger than you’d expect, like clams and mussels.
  • Feeling and Seeing: The starfish arms are super sensitive. They can feel and detect light, which helps sea stars figure out where they are and find their meals. It’s like having built-in GPS and night vision goggles all in one.
  • Healing and Growing: Starfish are the masters of regrowth. Lose an arm? No problem. They can grow it back and some can even grow a whole new starfish from just one arm. This incredible skill helps them survive attacks from predators and the rough and tumble of ocean life.

As evident in the list above, sea star arms are truly multipurpose tools that give these sea creatures everything they need to live underwater. 

Starfish Regeneration: Growing Back Lost Arms

Sea star regenerating its lost arms

Starfish regeneration is a fascinating process that allows these creatures to grow back lost arms and even parts of their central nervous system. 

According to a study published in Springer Link, it involves several intricate steps, beginning with the activation of special cells at the site of injury. 

These cells, which are known for their ability to repair and replace damaged tissues, undergo dedifferentiation (returning to a more primitive state) and transdifferentiation (changing into a different type of cell). 

Interestingly, sea star regeneration shares some common features with mammals, including humans. 

For example, the regeneration of the starfish nervous system involves the re-specification of existing neurons, which is a process also observed in human neural regeneration. 

This similarity extends to the molecular level since both starfish and humans utilize certain regulatory genes and proteins crucial for nerve regeneration. 

Additionally, starfish possess a unique cell type known as coelomocytes, which play a vital role in the initial response to injury. 

These cells are the ones that rush to the injury site and help protect the starfish from infection. They also heal the wound and kickstart the regeneration process. 

Their actions somehow resemble human platelets and immune cells, which converge on a wound to clot and protect against infection. 

Did this guide answer your question about how many arms a starfish has? Share your thoughts in the comment section below. Feel free to ask questions, too.

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