Have jellyfish got backbones

ANSWER:They have an exoskeleton. An exoskeleton is a skeleton made of water tubes which have tiny holes in them.

Actually chief...an exoskeleton is any form of skeleton on the outside of the organism. this can be chitinous (sort of like that hard shell on crayfish or "bugs" i.e. arthropods), hydrostatic (which is closest to what you are describing i.e. slugs, worms, etc.) and several others. A n exoskeleton can also be combined with an endoskeleton in organisms like fish(scales) and turtles(shells). There are several other types also which i do not know enough about to comment.

So yes, jellyfish have hydrostatic exoskeltons