Coelomic spaces in leeches serve as an auxiliary circulation system. The coelomic space and fluid have been transformed into a system with genuine blood vessels in leeches with a regular circulation system. In all the leech species, blood is transported from one location to another within the regular canal system of the coelomic space. Blood is conveyed with the contraction of the lateral longitudinal canals (Barnes, 1974; Çağlar, 1973; Davies, 1991; Demirsoy, 1982; Geldiayvd, 1991; Kastner, 1967; Sawyer, 1986).

Gills in leeches have been found only in some species of the Piscicolidea family. In other species, the body surface is suitable for a gas exchange. The branches of Piscicolidea are like natural lateral leaflets, or branched from the body wall. The gills are filled with spherical and spherical liquid. Respiration is ensured through the vibrating movements of gills. Leeches are also capable of respiration by fixing their posterior sucking discs swaying their bodies. Coelomic fluid in Gnathobdellida and Pharyngobdellida families include hemoglobin, which takes place in oxygen transport (Barnes, 1974; Davies, 1991; Demirsoy, 1982; Kaestner, 1967; Sawyer, 1986).