After having kept jellyfish as pets (Atlantic bay nettles), I wouldn't really consider them to be vegetarian nor vegan. While similar to plants, seemed to have a greater sense of environmental awareness than my plants. Mine could sense light, have "off days", and interact with their environment. It's probably true that there's not much going on there due to the small amount of nerves that control everything, but even when mine would accidentally get caught on tank cleaning tools or get bumped around they'd react in a protective way and to me it's just similar enough to animalistic behavior that I'd not feel comfortable consuming them if I were vegan.

I found a couple of articles on this:

“No.”

“it’s complicated.”

They have no brain but aren't they like almost entirely nervous system? That's all you need to feel pain; the brain just makes it more complicated than "ouch, move away from that."

No.

would u even get anything out of eating it tho?

No Brain? For Jellyfish, No Problem

“I think sometimes people use its lack of a brain to treat a jellyfish in ways we wouldn’t treat another animal,” Helm says. “There are robots in South Korea that drag around the bay and suck in jellyfish and shred them alive. I’m a biologist and sometimes sacrifice animals, but I try to be humane about it. We don’t know what they are feeling, but they certainly have aversion to things that cause them harm; try to snip a tentacle and they will swim away very vigorously. Sure, they don’t have brains, but I don’t think that is an excuse to put them through a blender.”

They're animals, so no.

A lot of Jelly fish are immortal? Just leave a few cells and wait for it to come back to life. Death-free food for the win

At this time it is impossible to know if they feel pain. They're a living creature.

Jellyfish eat animals and animal byproducts, so no, they are not vegan.

Jokes aside, often vegans follow dietary restrictions for reasons other than an ethical or moral belief against causing pain. Many vegans don't even eat honey, so I imagine jellyfish is pretty safely in non-vegan territory.

I believe that it is not, since scientifically it is an animal. However, some vegetarians (not vegans) will eat fish or certain animal products.

It depends on the definition of Veganism.

There’s is a popular school of thought that the diet‘s sole purpose to reduce suffering. If a living thing has no central nervous system (or brain), it has no thoughts and cannot experience pain or harm. It’s not much different than a fruit or vegetable. I know vegans that make exceptions for oysters - for example.

Others schools of thought are about avoiding animal products altogether, it doesn’t matter if it suffers or not - there’s no way to know. Therefore, it’s immoral to eat them if you can knowingly choose an alternative.