Creating the Skin

You make the skin by lathing a Bezier line. Start by drawing the skin around the inner anatomy of the worm.

Lathe the line in the X direction. Move the Lathe axis in Y to give it width as you did with the digestive system.

Apply an Optimze modifier. The default settings yield very satisfactory results:

Collapse the modifier stack of the skin. Your final model will look like this:

Creating the Worm's Food

Create a Capsule and add a Noise modifier to distort the surface and make it look bumpy. Place it directly in front of the worm's mouth.