CLASS HIRUDINEA

Leeches are among the most highly specialized of the annelids. They are predominantly freshwater organisms, although there are marine and terrestrial forms. Leeches are highly specialized predators that feed on blood. Some species are ectoparasites, that is, they live permanently attached to the skin or outer covering of another organism.

Examine the leech on display. Notice that the segmentation is not as noticeable as it was in the oligochaetes and polychaetes. At each end is a sucker, which the animal uses for attachment. Within the anterior oral sucker is the mouth. Leeches have jaws and chitinous teeth for biting. Leeches suck blood from the wounds they inflict, storing it in an enormous crop. A leech can ingest as much as three times its body weight at one "sitting", a meal which may last for as long as nine months. Leeches are hermaphroditic, but reproduction is usually by cross-fertilization; the reproductive process is very similar to that you have studied for the earthworm.