I. | Platyhelminthes | II. | Mollusca | III. | Annelida |
1. | Only I | 2. | Only II |
3. | Only II and III | 4. | I, II, and III |
1. | An open circulatory system | 2. | A closed circulatory system |
3. | A lymphatic system | 4. | A portal circulation |
I: | The body is divided into segments only externally. |
II: | There is a serial repetition of at least some organs. |
I: | is derived from embryonic mesoderm. |
II: | is present on the ventral side during embryonic development in chordates. |