SOME OBSERVATIONS ON CONCENTRICALLY STRUCTURED, INTRACELLULAR GRANULES IN THE HEPATOPANCREAS OF THE SHORE CRAB CARCINUS-MAENAS (L)

The R, F and B cells of the hepatopancreas of Carcinus maenas are derived from undifferentiated (E) cells at the distal end of the tubules. Observations with the scanning electron microscope on freeze fractured tubules show that (a) most of the concentrically structured granules are confined to the R cells with few in F or B cells, (b) within individual R cells, granules are of similar size, and (c) the further R cells are situated from the distal end of the tubule, the greater is the mean diameter of the granules that they contain. Observations with the transmission electron microscope show the importance of considering the plane of section through granules when studying their structure and composition. These observations strongly suggest that granules of the same size within individual R cells have the same internal structure. The composition of the concentric layers of the granules has been studied by X-ray microanalysis. Calcium, phosphorus and magnesium are always detected. However, in some animals, the layers also contain lead. In granules from these animals, layers of greater density contain more lead and to a lesser extent, more calcium and phosphorus. The outer layer of granules within individual R cells have similar composition. Since these granules are thought to have the same internal structure, it is suggested that analogous layers in different granules have the same composition. A scheme for granule formation is put forward. Granules are initiated within R cells at an early stage in their development. As each R cell matures and becomes more proximal in the tubule, all the granules grow synchronously by the periodic deposition of concentric layers of material. The importance of these granules in immobilizing calcium and other potentially toxic metal ions is discussed. It is concluded that the ability of Carcinus maenas to detoxify lead by incorporating it in these granules may be directly related to the number of granules which are immobilizing calcium in the hepatopancreas. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.