AbstractThe ultrastructure of the connective tissue spaces in the clitellar epithelium has been studied in the earthwormLumbricus friendi.Four morphological types of coelomic cells are described: amoebocytes, mucocyte‐like cells, pigment cells and crystal‐containing cells. The amoebocytes are characterized by the presence of spherical to oval electron‐dense granules, phagocytic vacuoles and numerous microtubules located in the Golgi areas. The mucocyte‐like cells show the features of the mucocytes reported in enchytraeid worms (globular inclusions with filamentous and homogeneous, moderately electron‐dense material, as well as a filopodous process). The pigment cells contain typical spindle‐shaped osmiophilic granules, microtubules (not reported before) and glycogen particles. The crystal‐containing cells show inclusions which are polygonal in section with a striated substructure (periodicity of about 4.5 nm). Apart from the mucocyte‐like cells, the coelomocytes showed cytoplasmic processes attached to the basement membrane of the spaces. The possible functions of these cells are discussed and a common peritoneal origin is postulated on the base of their morphological and cytol