Class Hirudinea - Classification of Coelom
These are leeches. Number of body segments of these types of animals is fixed; usually there are 34 segments in a few groups there may be only 31 or even 17. Segments have several annuli. Anterior and posterior sucker present, like also clitellum. No parapodia or setae. Coelom filled along with connective tissue and muscles. Hermaphrodites; direct development, may be terrestrial, fresh water or even marine. The leeches differ in size from 2-6 cm in length, and are flattened dorsoventrally. The clitellum, although present, appears only during breeding season. Their gut is extremely specialized for storage of blood. Though they have only 34 segments, since the segments are marked by transverse grooves they appear to have much more rings (annuli). With regard to coelom, the septa have disappeared, and the coelom is filled along with a connective tissue (botryoidal tissue). The remaining spaces termed as lacunae are filled with coelomic fluid.