The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream (Sparus aurata) intestine and sharpsnout sea bream (Diplodus puntazzo) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant β-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum.

This study was funded by the European Union through a re-search project QLRT-2001-00722 (MyxFishControl). We aregrateful to the staff of the Electron Microscopy Services of theUniversitat Autonoma de Barcelona, Universitat de Barcelona,and Universite´Montpellier II–-Sciences et Techniques duLanguedoc. M. Cuadrado was recipient of a research grant fromthe Departament d’Universitats, Rec erca i Societat de la Infor-macio´, and the European Social Fund

Peer reviewed