Leech image courtesy of Worm World

The final major class in phylum Annelida, class Hirudinea, consists of the leeches. Leeches are known for sucking the blood of humans, but most are free-living and eat small invertebrates, feeding on their blood. Most live in freshwater environments, although a few can live in terrestrial environments. Like earthworms, leeches are hermaphroditic and lack appendages. To successfully drink the blood, they have a small sucker in the anterior end and a larger one in the posterior end.

Hirudineans are in the phylum Annelida, made up of segmented worms. Body segmentation, a hallmark of annelids, was a major step in the evolution of animals. Annelids are protosomes, meaning they have a coelom made from cell masses. This coelom is divided into a series of repeated parts. Except for the head and tail region, each with an opening of the digestive tract, making it a complete tract, each segment in an annelid is ringlike and very similar. Segmentation allows for flexibility and mobility because annelids can bend at segmented parts. Other hallmarks of the annelids are soft bodies that are round in cross section, repetition of organs in the segemented parts, and a body that is much longer than it is wide. There are three main classes in the phylum Annelida.

Information provided by: http://www.sidwell.edu