Coelomocyte Morphology in the Holothurians Apostichopus japonicus (Aspidochirota: Stichopodidae) and Cucumaria japonica (Dendrochirota: Cucumariidae)

The cellular composition of the coelomic fluid of the Far Eastern holothurinans Apostichopus japonicus and Cucumaria japonica was studied using light and transmission electron microscopy and histochemistry. In the coelomic fluid of A. japonicus, the following types of coelomocytes were distinguished: progenitor cells; amoebocytes; vacuolated cells; small (or young) morula cells; morula cells of type I, type II, and type III; crystal cells; and vibratile cells. In the coelomic fluid of C. japonicawere found progenitor cells, amoebocytes, vacuolated cells, morula cells of type I and type II, crystal cells, and hemocytes containing a respiratory pigment. The issue of stem cell type, which gives rise to coelomocytes, is discussed.