THE ULTRASTRUCTURE OF HEMOCYTES IN TROMBICULID MITES (ACARIFORMES, TROMBICULIDAE)

The ultrastructure of haemocytes during the entire ontogenesis in Hirs utiella zachvatkini (Schluger) and in pre-larvae and unfed larvae in L eptotrombidium orientale (Schluger) was investigated using transmissio n electron microscopy. Two, fine- structurally distinct types of granu lar cells, namely granulocytes of types I and II, were observed. The g ranulocytes of both types are oval to amoeboid and contain numerous sp ecific granules, their most characteristic feature, in addition to oth er cell organelles. No changes in the structure of the haemocytes duri ng the development of the mites were observed. The granulocytes are mo st abundant in quiescent stadia in the life cycle and in particular du ring moulting, when they migrate in large numbers to the exuvial space , develop pseudopodia-like processes on the cell surface, which are th e most distinguishing feature of type I granulocytes and, finally, dis integrate and release their granules into the exuvial space. Within th e cytoplasm of type II granulocytes, large crystals, presumably of hae mocyanin, are accumulated. Prohaemocytes have not been identified as a distinct cell type. The possible functions of the haemocytes and also their structure and differentiation in comparison with other arthropo ds are discussed.