What makes up the hydrostatic skeleton of an earthworm (annelid)?

The hydrostatic skeleton of an earthworm, which is an annelid, is made up of the following components:

1. Coelomic Fluid: This is the primary component of the hydrostatic skeleton. The coelomic fluid is a liquid that fills the coelom, a cavity within the body of the earthworm. This fluid is under pressure and provides the worm with a rigid structure.

2. Body Wall Muscles: Surrounding the coelomic fluid are layers of muscles. These muscles contract and expand to control the shape and movement of the earthworm. There are two types of muscles involved: circular muscles that wrap around the body of the worm, and longitudinal muscles that run along the length of the worm.

3. Septa: These are thin walls of tissue that divide the coelom into segments. Each segment is filled with coelomic fluid and can be controlled independently by the worm. This allows for precise movements and flexibility.

4. Cuticle: This is a thin layer of non-cellular material that covers the exterior of the earthworm. It provides protection and helps to maintain the shape of the worm.

Together, these components form a hydrostatic skeleton. This type of skeleton allows the earthworm to move and change shape without the need for hard, rigid structures like bones.