Earthworms do not have a skeletal system in the same way that vertebrates do. They lack bones and a rigid internal framework. Instead, they have a hydrostatic skeleton.

Here's how it works:

* Fluid-filled body cavity: Earthworms have a coelom, which is a fluid-filled body cavity. This fluid acts as a hydrostatic skeleton.

* Muscles: They have both circular and longitudinal muscles surrounding their body.

* Movement: When the circular muscles contract, the worm becomes longer and thinner. When the longitudinal muscles contract, the worm becomes shorter and wider. This alternating contraction of muscles against the hydrostatic pressure of the coelomic fluid allows them to move and burrow.

* Support and protection: The hydrostatic skeleton also provides support and protection for the earthworm's internal organs.

Therefore, while earthworms lack bones, their hydrostatic skeleton allows them to move, maintain shape, and protect their internal organs.