Most jellyfish species have rhopalias that act as eyes to help the species see well enough to move properly. Among all the common species, only box jellyfish have eyes exactly like other animals for better vision. Apart from box jellyfish, many others can only see blurry images and changes in light with the help of rhopalia or eye spots.
Although jellyfish are one of the most ancient surviving creatures on this planet, they’re not fully developed to have specific organs for each biological activity like other animals.
But jellyfish have a bundle of strong nerve chains that allows several activities like sensing light. The only clear exception in this topic is box jellyfish. The others can’t fully understand the proper shape of anything in front.
Do Jellyfish Have Eyes and Mouths? How Many Eyes Does a Jellyfish Have
Yes, jellyfish have something that can work like human eyes, but they’re not specifically eyes in general. Also, they have only one opening in their body that can work, like both mouth and the exit point of waste after eating.
There are many jellyfish species that hunt down several other small species under the sea. So obviously, they must have a sensing system for vision to find out prey and move accordingly.
Although the vision system in the jellyfish anatomy isn’t specific and doesn’t have any dedicated organs, the system is strong enough to sense what’s in front and how it’s shaped.
The rhopalium is a combination of several nerves that can detect light and the change in light. With the help of this blurry instinct, jellyfish roam in groups and survive for years.
People who are well aware of sea biodiversity already know that jellyfish mostly contain water in their bodies. They belong to the cnidaria group, and for that, these gelatin-like creatures don’t have dedicated organs like hearts, brains, bones, eyes, mouths, etc.
The main body, also known as a bell, can have multiple openings. But these openings work as both mouth and anus. Due to having a very compact and simple anatomy, jellyfish eat and poop using the same space.
This so-called mouth and anus are right under the bell, with tentacles decorated on every side. The tentacles work as hands to grab and take the food inside the mouth. And the rest is done by the bell.
How Do Jellyfish See Without Eyes Like Us?
Obviously, jellyfish can’t see like humans as their visual system isn’t well-developed or specified. The highest activity by the rhopalia or vision system is to sense the changes in light in front. Apart from that, rhopalia fail to send the exact picture of objects in the main nerves.
By just sensing the amount or intensity of the light through rhopalia, jellyfish can decide what the next activity or movement should be. That’s why most jellyfish can’t exactly decide what’s in front or how the nearby object’s going to act.
What Is the Rhopalia Function in The Jellyfish Body?
Rhopalia is actually a combination of nerves or neurons inside the jellyfish bell. There are ectodermal connections between multiple connections inside a bell. All the connections lead to the main nervous system in the bell, which decides the movement of the whole body.
Usually, rhopalias stay at the edge of the bell-like human eyes located in front of the face. In the rhoplaia, you can find photoreceptors that dedicatedly calculate the light intensity to help the main nervous system take and decide against the light intensity.
As rhopalia aren’t any completely formed organs, they can’t work like human eyes. So, no matter how close a person gets to the jellyfish, it can never detect you as a human. But it might sting you when the rhopalia find any change in light is coming very close.
Do Box Jellyfish Have Eyes Like Humans? How Many Eyes Does a Box Jellyfish Have?
Box jellyfish have the most developed vision system among all the jellyfish and cnidaria species. You can find eyes just like ours in the box jellyfish’s body floating inside the bell.
These eyes are not only like ours, but they also work like human eyes too. Several researchers have stated that box jellyfish can specifically identify what’s in front and how things are moving around it.
But it’s also true that those eyes aren’t completely developed. The images received from box jellyfish eyes might be a bit blurry, yet clear enough to make the box jellyfish a carnivore species.
Normally, box jellyfish have 24 eyes in several sets, which makes these creatures more dangerous. They can make quite the right decisions, including what to sting and how to avoid attacks.
Can Jellyfish Have Eyeballs?
Only box jellyfish have something that you can compare with eyeballs. Those floating bubbles inside the bell might not exactly look like eyeballs, but they contain retinas, lenses, etc.
If we consider their eyeballs, then box jellyfish have 4 eyeballs, with each containing 6 eyes for different purposes. Among those 6 eyes in each set, 2 have lenses just like we have. And for that reason, jellyfish can almost see like other fishes underwater.
FAQ
Can jellyfish see you?
Most jellyfish won’t see you properly even if you stay closer. But they’d surely detect your presence and take some action against your presence. In a way, jellyfish can see you a little bit.
Why do only box jellyfish have eyes?
Jellyfish Kind have lived for more than 600 million years. Among the jellyfish species, only box jellyfish were able to develop their eyes, as they’re known for their carnivorous instincts. Because they need to hunt, move, and work precisely, this specie has developed 24 complex eyes.
How many sensory organs do jellyfish have for vision?
The whole sensory system for vision in the jellyfish body is known as rhopalia. This combination is the only section of the jellyfish anatomy that deals with light intensity.
Do moon jellyfish have eyes?
No, moon jellyfish also depend on nerves to sense light, just like hundreds of other jellyfish species. Moon jellyfish have rhopalias too, to sense the light and anything moving in front.
Summary
Jellyfish can see, even if it’s not enough like other beings. If they were unable to see, they wouldn’t be able to move and live in groups like other social fishes.
Only box jellyfish have the organs that we generally call eyes. Except for that, any other jellyfish type doesn’t have a dedicated vision system developed in their bodies.
Rhopalia is just a group of nerves and neurons attached to the main nerves to send the changes in light in the surroundings. Thus, rhopalia can’t be considered as eyes.
Resources:
https://www.scienceabc.com/nature/animals/do-jellyfish-have-eyes.html#:~:text=With%20these%20eyes%2C%20Tripedalia%20cystophora,of%20mangroves%2C%20or%20find%20prey.
https://www.youtube.com/watch?v=72mLOTVuaiw
https://www.livescience.com/7243-jellyfish-human-eyes.html
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