Describe the digestive system of a leech with a labelled diagram.

1. 1 · Open in one line. The leech has a straight alimentary canal from mouth to anus, built to suck and store blood.
2. 2 · Draw and label. [Mouth, jaws, buccal cavity, pharynx, salivary glands, oesophagus, crop chambers, crop caeca, stomach, intestine, rectum, anus]
3. 3 · Front parts.
   • Mouth in the anterior sucker.
   • Buccal cavity with three jaws bearing fine teeth; they cut a Y-shaped wound.
   • Muscular pharynx sucks blood; salivary glands secrete hirudin.
4. 4 · Storage. A short oesophagus opens into the crop, the largest part, with 10 chambers and paired caeca; it stores blood for months.
5. 5 · Digestion and absorption. Blood is digested slowly in the stomach and absorbed in the intestine; the rectum opens by the anus on the dorsal side of segment 26.
6. 6 · Real life. Because hirudin stops clotting, a leech bite keeps bleeding for a while; hirudin has guided the design of anti-clotting medicines.
7. 7 · Close in one line. So the gut of a leech is a store-house that lets it live long on a single meal.

Scoring tip: Label the jaws, salivary glands and crop caeca; they also show the parasitic adaptations.