Ultrastructure and microanalyses of the calcareous corpuscles of the protoscoleces of Echinococcus granulosus.

The calcareous corpuscles of the protoscolex stage of Echinococcus granulosus are irregularly spherical or ovoid in shape and have a diameter ranging between 2 and 16 microns. The central region of immature corpuscles is composed of an electron-lucent matrix containing granular deposits and, in more mature corpuscles, paired membrane lamellae. Energy-dispersive X-ray microanalysis of sectioned immature corpuscles demonstrated calcium, magnesium and phosphorus, whilst a quantitative analysis indicated the presence of calcium and magnesium at 142.7 and 41.3 mg/g dry weight, respectively, and inorganic phosphate at 18.0 mg/g. Assuming that the anion is predominantly carbonate, the molar ratio of Ca:Mg:HPO4(2-):CO3(2-) is 1:0.48:0.08:1.41. X-ray diffraction patterns obtained from preparations of whole corpuscles indicated a poorly crystalline material including the mineral calcite. X-ray absorption near-edge spectra of corpuscles, taken over the phosphorus K edge, resembled those of brushite (CaHPO4.2H2O) and suggest that the phosphate, within the corpuscles, is present in an amorphous, hydrated form that could be readily solubilised and mobilised for the metabolic processes of the organism.