Comparative Analysis of Calcareous Corpuscle Morphogenesis in Amphilinideans and Eucestodes, With Insights Into Some Atypical Ultrastructural Characteristics of the Amphilinidea (Cestoda)

ABSTRACT

Calcareous corpuscles are present in the myocytes of eucestodes, yet little is known about their formation, and amphilinidean cestodes have not been investigated in this respect. Here, we present an ultrastructural study of the calcareous corpuscles and their formation in adult Amphilina foliacea , a parasite of the body cavity of the sterlet sturgeon Acipenser ruthenus and several eucestode species. Ultrastructural differences are shown to occur between the morphogenesis of calcareous corpuscles in this amphilinidean and adult bothriocephalideans, Triaenophorus nodulosus , Eubothrium rugosum and Paraechinophallus japonicus , an adult cyclophyllidean, Shipleya inermis , and plerocercoids of the phyllobothriidean Clistobothrium sp. In all of the cestode species studied, the formation of calcareous corpuscles takes place in myocytes. Unlike eucestodes, in which corpuscle formation occurs within a sarcoplasmic vacuole with the displacement of the nucleus to the cell periphery, in amphilinideans their formation is intranuclear and occurs in two sites. Firstly, within the myocytes of parenchymal muscle fibers, with the autophagic disruption of both nucleus and sarcoplasm, and a subsequent karyoplasmic and sarcoplasmic formation of one corpuscle per myocyte. Secondly, corpuscle formation occurs in storage myocytes, beginning within the nucleus. The possible functions of calcareous corpuscles are discussed in relation to the environmental needs of the parasite. Atypical ultrastructural characteristics of amphilinideans support current opinions concerning the long evolutionary history of these enigmatic cestodes.