Sipunculus nudus: particulate components of the coelomic fluid and its relationship with brown bodies

Corpuscular components of the coelomic fluid were observed in Sipunculus nudus using cytochemical and cytoenzymatic methods. In particular, granulocytes were studied and two different types, based on morphology, chemical composition, and function were distinguished. Cell aggregates, identified as stem cells of type II granulocytes, were also evidenced. Besides, empty vesicles, vesicle fragments, laminar structures and brown bodies were observed. Based on the observation of their structure and ultrastructure, brown bodies were attributed with the function of accumulating foreign material, as well as aged components typical of the coelomic fluid.