Final answer:
Earthworms have a hydrostatic skeleton, which is a fluid-filled system that allows them to move by peristalsis. Unlike exoskeletons seen in crabs and insects, the hydrostatic skeleton does not require shedding to accommodate growth.
Step-by-step explanation:
The type of skeletal system that earthworms have is a hydrostatic skeleton. Earthworms move by waves of muscular contractions of the skeletal muscle of the body wall hydrostatic skeleton, which is a process called peristalsis. This type of movement includes alternately shortening and lengthening the body, which helps in their locomotion. Organisms with hydrostatic skeletons, such as earthworms, must shed and regenerate their skeletal system as they grow. These organisms, like earthworms, move by extending their body in one direction and then shortening to pull themselves along a surface.
The hydrostatic skeleton is a fluid-filled compartment held under hydrostatic pressure, and the pressure exerted by the fluid contents causes movement when the surrounding muscles contract. This is in contrast to an exoskeleton, which is a hard external skeleton found on organisms like crabs and insects, and an endoskeleton, which is an internal skeleton found in organisms such as humans and other vertebrates.