Only under unusually specific conditions would a soft-bodied creature such as a jellyfish be capable of making a fossil. If deposited in an extremely fine suspension of mud, and presuming that there were no scavenging organisms present.
Such fossils are known, and you'll find some data in wikipedia under Ediacaran.
A clam.
Jellies have no bones. When they die, they just dissolve.
They do not have any bones. No bones means there is nothing to fossilize.
because they don't have any bones or solid structures to fossilize
A clam is more likely to fossilize than a jellyfish.
Jelly fish don't have bones or teeth which are typically what fossilizes. Jellyfish are mostly water so they decompose extremely easily. Its like trying to fossilize soggy jello. They live in open oceans so its difficult for a jellyfish to become fossilized when there isn't a whole lot of soil around.
A clam is more likely. Jellies have no bones.
Dinosaur bones are made of hard, durable material like calcium phosphate, which is more resistant to decay than the soft tissue of jellyfish. Jellyfish are composed mainly of water and soft tissues that decompose quickly, making it harder for them to fossilize. The conditions needed for fossilization, such as rapid burial and protection from scavengers, are more likely to occur for hard, mineralized bones than soft-bodied organisms like jellyfish.
A mammoth is more likely to fossilize than a caterpillar because a caterpillar has no hard tissue. Bones and cartilage are much more likely to fossilize.
To scare. Or to fossilize.
Bones typically fossilize the most. There are some examples of fossilized feathers and hair, but it's rare.
Only under unusually specific conditions would a soft-bodied creature such as a jellyfish be capable of making a fossil. If deposited in an extremely fine suspension of mud, and presuming that there were no scavenging organisms present. Such fossils are known, and you'll find some data in wikipedia under Ediacaran.