Here's some ideas that could make jellyfish-girls fun.
They can clone themselves:
Jellyfish can reproduce either sexually between male and female, or by cloning themselves, which could open up some rather scenarios. If males are as rare as for the the rest of Felaryan species, the bulk of jellyfish-girls would be clones of some rare 'original'. Friends of a jellyfish-girl are then likely to run into "that" person many times in different places.
But as it's one's life that effects a large part of who a person is, clones could become slightly different. In a way the clones of a person would show her possible outcomes.
They can morph back into a child:
A few jellyfish can regrow from the adult state to the first larva state, which makes them in theory an immortal animal. For a jellyfish-girl this could be like an adult who suddenly turns into a child.
If they're still a grownup in a child's body or become immature again could be debated. It would still make friendships pretty awkward though if it was something that happened a lot.
Being immortal, these jellyfish-girls fit as wise old sage characters, as they would've picked up a lot of knowledge theory the years. An idea could be that a few have been alive since Felarya was created.
Stinging tentacles :
They couldve hanging appendages which stings, just like jellyfish, used both to give a painful sting to a same sized enemy, or to paralyze smaller creatures when hunting.
It would be funny if they'd floated around rather freely in the water, something they must remember to be mindful of, which would probably probably put anyone nearby on the edge.
They would be slow swimmers and their bodies would be fragile and easily raptured, so they'd probably try to avoid violence. Like real jellyfish they would be able to heal any kind of injury and regrow lost limbs.
If they would some kind of culture, it could maybe revolve around knowledge and wisdom, or their ability to make light in different colors, which could be a sort of performance art. An idea I think is cool is of an "orchestra" of jellyfish-girls, led by a conductor, and instead of music they perform a complex show of colorful light. Some of them would be the artsy, eccentric writers of these pieces too.
Jellyfish are beautiful and there's a wide variety of looks. This would give plenty of inspiration for unique characters.
The transparency, colors and lights would them look pretty different. Some might think they look beautiful and even angelic, and to others they probably looks more like living gelatin candy.
Maybe a rumour could be that they should taste like jelly..
A basic design could like an octopus-girl, with the round bell-shaped thing like a skirt around her waist, and the stinging things hanging from her lower center, which funnily enough would probably be where the genitalia is located...!
As for hair, it would probably be a little different and look very shiny.
Their transparence would be fun when it comes to eating. A little different
So what do you think?