Earthworms
The Earthworm does not contain a bone skeleton nor a cartilage. They have a "hydrostatic skeleton, which consists of a fluid-filled cavity, the coelom, surrounded by muscles. The pressure of the fluid and the action of the surrounding circular muscles are used to create the shape of the worm and prevent the worm from collapsing on itself. Its shape changes whenever it swims, burrows itself underground, etc.
Ragworms
Ragworms have the similar system as the Earthworm. The only difference is its appearance, shape, and location. Also it has small cirri to move around. The pressure of the skeleton makes it more flat and pressurize the cirri for movement.
Leeches
Leeches are usually more round and fatter than the other two worms, yet it also has a hydro-skeletal system. Since the Annelids have a hydro-skeleton, they are pretty sensitive and can get crushed easily because the skeleton only helps to keep the gravity from making the organs to collapse.