Three cross-sections of worm-like animals are shown under a microscope.

Three cross-sections of worm-like animals are shown under a microscope.

1. Section P: mesoderm lines the body wall and also covers the gut, with a fluid-filled space between.

1. Section Q: there is a space around the gut, but mesoderm appears only in a few pouches under the body wall.

1. Section R: mesoderm cells fill all the space between the body wall and the gut.

Name the kind of body cavity in each, and a phylum that fits.