E. hepatopenaei has several features similar to E. bieneusi, the
only current member in the genus Enterocytozoon (Franzen and
Müller, 1999). For both species, the sporogonal plasmodium is
localized in the host-cell cytoplasm and it generates pre-cursors
of the spore extrusion apparatus prior to the formation and budding
of sporoblasts. For both, sporoblasts are liberated to the host
cytoplasm following which they develop directly into oval spores.
Other similar morphological features included spores with a posterior
vacuole and 5–7 coils of polar filaments arranged in two
rows (Franzen and Müller, 1999; Wasson and Peper, 2000; Visvesvara,
2002; Didier, 2005). However, the mean spore size of E.
hepatopenaei (1.1 0.7 lm in fresh preparations) was somewhat
smaller than that of E. bieneusi (1.5 0.5–1.0 lm) (Franzen and
Müller, 1999; Didier et al., 2000; Wasson and Peper, 2000),
although the difference was not great, and it might be argued that
it was not sufficient to warrant designation of two separate
species.