(ă-nĕl′ĭ-dă)
[Pronunciation]

The phylum that includes earthworms, leeches, and other segmented worms.
Some annelids are intermediate hosts for parasitic worms. Leeches are ectoparasites. The medicinal leech, Hirudo medicinalis, is the source of an anticoagulant that is used to treat myocardial infarction and other conditions caused by blood clots.