Structure and development of a marine actinosporean, Sphaeractinomyxon ersei n. sp. (Myxozoa)

This is the first ultrastructural study of the development of a marine actinosporean and of a species belonging to the genus Sphaeractinomyxon Caullery & Mesnil, 1904. S. ersei n. sp. is described from a limnodriloidine oligochaete, Doliodrilus diverticulatus Erseus, 1985, from Moreton Bay, Queensland, Australia. Development is asynchronous, there being all stages from two-celled pansporoblasts through to mature spores present simultaneously within a host. Sports develop in groups of sight within pansporoblasts In the coelom and when mature are located also in the intestinal lumen. The primordial spore envelope and sporoplasm develop separately in the pansporoblast until the polar filament is formed within the polar capsule and the capsulogenic cell cytoplasm has begun to degrade. The sporoplasm then enters the spore through a separated valve junction. Mature spores are triradially symmetrical with three centrally located polar capsules and a single binucleate sporoplasm with about 46 germ cells. Swellings or projections of the epispore do not occur when spores exit the host and contact sea water.