The ultrastructural identity of Protoentospora ptychoderae Sun, 1910 (Apicomplexa, Coccidia), a parasite of the body cavity of the enteropneust Glossobalanus minutus (Kowalewsky, 1866): Growing trophozoites.

The ultrastructural organization of Protoentospora ptychoderaeSun, 1910 from the coelom of the enteropneust Glossobalanus minutus (Kowalewsky, 1866) is presented. The parasites, identified as growing trophozoites without parasitophorous vacuole, are typical Apicomplexa with a trilaminate pellicle perforated by a micropore. The apical structures which characterized the infective forms of this group (apical rings, conoid, rhoptries, micronemes and subpellicular microtubules) gradually disappear throughout the trophozoite development. The cytoplasm contains mitochondria with vesicular cristae, a well developed Golgi apparatus, free ribosomes, smooth and rough endoplasmic reticulum, and large stores of amylopectin and lipids. The nucleus has a prominent, eccentric nucleolus. The systematic position of Protoentospora is discussed from the present data and the available literature.