[1] The defining feature of this genus is their development, after becoming enclosed by extensions of the host cell membrane, within the resulting parasitophorous 'sack' which bulges out above the surface of the intestinal mucosa.

Below the parasitophorous vacuole, the host cytoplasm expands as the volume of the parasite increases, giving rise to a short, stalk-like structure.

Meront: These possess all the typical features of the Apicomplexia including an apical complex, sub-pellicular tubules and micronemes.

Young meronts are bound by a single membrane, and contain large mitochondria and a few micronemes.

The macrogamonts are bound by a single unit membrane, coated by a variable amount of glycocalyx.