RESUMO
Mesocestoides corti (syn. vogae), similar to many other cestode platyhelminthes, contains abundant calcium carbonate structures called calcareous corpuscles. These concretions that may constitute as much as 40% of the dry weight of the body, and were proposed to form intracellularly in certain parenchymal cells. As an approach to elucidate the biological role of calcareous corpuscles in cestodes, our aim was to characterize more precisely the structure and topological composition of the corpuscles from M. corti. Employing a variety of high resolution technical approaches, we found that the calcareous corpuscles are spheroid or ovoid layered concretions. They are formed by topographically homogeneous but compositionally heterogeneous layers, suggesting a cyclic process of biomineralization. The layers are composite structures, with granules of tens of nanometers, each surrounded by a cortex of about eight nanometers.