What is the hirudinea and oligochaeta?

Hirudinea are leeches. many are predators that feed on other invertebrates, but some are parasites that suck blood. body usually flat, chaetae(each segment has 4 pairs of chaetae, bristles that provides traction for burrowing) absent, sucker at anterior and posterior ends, parasites, scavengers.

Oligochaeta: freshwater, marine, and terrestrial segmented worms such as earthworms, reduced head, no parapodia, chaetae present. ^_^