Do Starfish Have Brains? (Explained)
Starfish, or sea stars – the term scientists prefer because the invertebrates aren’t actually fish – are generally simple animals without blood or obvious organs to walk or see. A lot of people wonder if these marine creatures have an actual brain.
In this article, we’ll talk all about that but let’s start with a quick answer:
Starfish don’t have brains that we know but they do have a nerve ring that is an essential part of their bodies’ system. This ring connects radial nerves running the length of each arm of the starfish that can react to the stimuli.
However, that certainly doesn’t tell the whole story. Below I’ll explain more about starfish’s “brain”, explain how their nervous system work, and tell you more about how starfish can possibly experience pain. Read on!
Starfish don’t have a brain that we know, but they do have an essential part of their body system called the nerve ring. It surrounds the mouth and connects radial nerves running the length of each arm of the starfish. This creates a sea stars’ nervous system, similar to other Echinoderms nervous systems, such as sand dollars, sea urchins, or brittle stars.
The nerves later control all the starfish movement, react to the stimuli, store all the information, memories, and any decisions about what to do. In addition to that, they coordinate those decisions together.
How do starfish share sensory information without brains?
Sensory information can be shared between starfish tube feet. It’s fascinating that starfish thousands of tube feet can react autonomously to the stimuli. However, when starfish are walking, they can synchronize them and create a bouncing motion – all without a technical brain!
For example, an adult sunflower sea star can coordinate its tube feet and move one meter per minute using 15000 tube feet at the same time!
Tube feet are small flexible appendages located on the underside of sea stars’ bodies. They’re controlled by a water vascular system – a system of canals that connect each tube foot. When the water comes into the system, tube feet extend and reach. When the water goes out, suckers on the top of each foot create a vacuum and help to attach the tube foot to the surface.
It’s also interesting to note about sensory information shared between the different arms and that each arm can take charge of the whole starfish. When starfish is moving, there’s most likely one arm in front. This arm directs movements and seems to take charge of the sensations, like odor or light.
In other words, the sea star has a dominant arm that leads the way and provides instructions on which way to move. Next, thousands of tube feet follow to achieve what was communicated.
Another interesting fact about senses is that starfish have eyes on the very tip of their arms. Thanks to them they can see light, dark, and large structures. Their eyes primarily help them to find a way home – coral reefs.
If you’re interested in reading more about this, I wrote a blog post about starfish eyes here.
As you can see, despite a lack of brain, starfish can thrive. They can locate their food, find their mates, and even can distinguish different odors, ignoring those which are not associated with food.
Do starfish feel pain?
Knowing that certain animals don’t have brains makes us wonder if they can feel pain. As we already know, starfish don’t have a technical brain, but they have a nervous system with a central ring, so they can definitely feel something.
They most likely experience pain another way we do, but we’ll probably never know exactly how. However, scientists studied pain in invertebrates, so the results are worth mentioning.
How can we identify pain in animals?
We can define a few categories that can evaluate the potential for pain in animals. The first is their anatomy. Based on science, animals should have a suitable nervous system and sensory receptors to be able to feel. They detect sensory information and communicate it with the body.
The second is behavioral responses, such as limping, rubbing, or nursing wounds. Just like humans, when animals feel pain, they automatically rub part of their body that is irritated.
The third is long-term behavior changes. Animals can show a difference in their behavior after experiencing a painful event exactly as humans do. For example, after touching fire, we know we should not do that anymore because it causes us pain.
Knowing these categories, let’s now look at studies on how invertebrates reacted to noxious stimuli and how we can compare it with starfish.
Studies on invertebrates
Professor Robert Elwood has been looking for ways to answer the questions if invertebrates feel pain and he conducted a lot of research, mostly on crustaceans. One of the examined animals was prawns.
He brushed their antennae with acetic acid, and they began grooming their treated antennae with complex movements of both front legs. Furthermore, their rubbing movement decreased when scientists applied a local anesthetic before the experiment.
Another animal the professor examined was a crab. He applied a brief electric shock to a part of the hermit crab body. He noticed the crab rubbing that sport with its claws for a long time.
In our case, however, sea stars don’t have apparent organs to rub their wounds, as crabs do. However, what’s interesting is that Robyn Crook, an evolutionary neurobiologist, examined squids, and noticed that they might experience pain entirely differently.
Right after a squid’s fin was crushed, nociceptors became active, but not only where the wound was. They became active across a large part of the squid’s body, extending to the opposite fin. It could suggest that if this animal feels pain, it may hurt all over, rather than feeling it in one spot.
We’re not sure yet why this would happen, but it makes sense from the animal’s perceptive. The squid’s tentacles can’t reach many parts of its body, so it couldn’t even tend its wound. What’s more, squids are forced to move all the time because of their fast metabolism and keep hunting.
An injured squid with all-over heightened sensitivity may stay more alert and sensitive to touch and visual stimuli. “Its long-term behavior changes,” she says. “This fulfills one important criterion for pain.”
How do starfish experience pain?
There was no research on starfish yet, but we can definitely draw a conclusion based on previous research and sea star anatomy. We know that sea stars have a nervous system, so they’re capable of feeling.
The previous research also proved that invertebrates respond to noxious stimuli by behavioral and long-term motivational changes, so they most likely feel pain. Read more about it in my other post: “Do Starfish Feel Pain?”.
We’ll probably never know how exactly starfish experience pain, but we should always keep in mind that sea stars, just like other animals, are living beings and deserve ethical consideration.
Keep that in mind when you see sea stars by the shore or in the water when diving and never touch anything underwater. You can not only cause animals to feel pain but also transfer diseases.
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