Hemolymph cells and the platelet-like structures of the land slug, Incilaria bilineata (Gastropoda: Pulmonata)

3 morphologically distinct hemolymph cell-types, Types I, II and III, were found by light and electron microscopy of hemolymph from the land slug, Incilaria bilineata. In addition, vast numbers of the platelet-like structures were present in the collected hemolymph. Type I cells were macrophage-like, Type II cells were lymphocyte-like and Type III cells were fibroblast-like. Among these hemolymph cells, only Type I cells could recognize foreign materials and phagocytose them. Type I cells, whether from circulating hemolymph or from the heart-kidney region (regarded as a hemopoietic organ), could be maintained for only 4 d in cultivation because the cells gradually divided within 3 or 4 d. Thus, the platelet-like structures appear to be derived from Type I cells, which readily fragmentize and function by clamping onto foreign materials.