Earthworm (Pheretima): Every Organ by Segment Number

In the paper

Unit 4 (Study of Selected Animals) carries 6 of the 40 zoology marks, and with three chapters sharing them, the earthworm averages about two (MEC publishes weights by unit, not by chapter). The MEC scope line reads Morphology, Different body systems and physiology, Economic importance. Almost every earthworm question is a segment number in disguise, so this note is built around the table at the end. The paper (set 50:30:20) asks it in four ways:

• Recall — "the clitellum occupies segments...", "hearts are found in segments...", "the typhlosole begins in segment...".
• Understanding — why a hermaphrodite still cross-fertilises, why haemoglobin in plasma still makes a closed system, why septal nephridia open into the gut.
• Application — a cut worm regrows its tail but not its head; worms on a pavement after rain; a vermicompost bin that turns sour.
• Odd one out — three structures in the same segment and one that is not.