Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Hirudinea. Like other oligochaetes

Oligochaeta

Oligochaeta is a subclass of animals in the biological phylum Annelida, which is made up of many types of aquatic and terrestrial worms, and this includes all of the various earthworms...

 such as earthworms, leeches share a clitellum

Clitellum

The clitellum is a thickened glandular section of the body wall in earthworms and leeches, that secretes a viscid sac in which the eggs are deposited...

 and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways. For example, leeches do not have bristles and the external segmentation of their bodies does not correspond with the internal segmentation of their organs.