There are alot of differences between these two marine creatures.
Just generally:
Turtles are a reptile that have the trunk of their bodies encased in a hard shell.
Jellyfish are umbrella looking and have soft gelatine-like (jelly) bodies. They have tentacles trailing from the bottom, which in some species can be toxic.
ADDED. Another difference: predator and prey. Turtles, or some species of them at least, eat jellyfish! This explains the distressing number of turtles dying having mistaken floating polythene bags for jellyfish.
Well First thing a jellyfish is squishy and a shellfish is rock solid (so I've been told).
ADDED. Both animals are "squishy"! The difference is that the shellfish wraps itself in a hard shell - but it's not rock-solid.
No
jellyfish sting
Fish have fins and scales, shellfish do not. Shellfish are crustaceans ... totally different species from fish.
A jellyfish is a marine creature. A guitar is a musical instrument.
Jellyfish
A jellyfish lives underwater and a frog lives on a leaf in the water or on land.
fish jellyfish plankton sponges slugs and shellfish
fish, seastar, seahorse, whale, shark, squid, jellyfish, sponge, shellfish
First of all, the man-of-war is not a true jellyfish. Its body is filled with air. To be a jellyfish the "bag" of their body has to be filled with water. Also a box jellyfish is more dangerous. The box jellyfish is the most dangerous jellyfish in the world.
Coral Reefs don't really move and jellyfish move around, and sting people. Coral Reefs help other thins in the sea survive, where as jellyfish don't. The jellyfish are just there.
A shrimp is a shellfish. Although there's a little difference between them. They are pretty different even if they are Shellfish. Some people are Allergic to Shellfish and they aren't allergic to Shrimps.
A human nervous system is much more complex. Unlike a human a jellyfish does not have a central nervous system.