Wikipedia
Gemmocystis
Rhytidocystis is a genus of apicomplexan.
This genus is parasitic on scleractinian corals ( Agaricia agaricites, Dendrogyra cylindrus, Diploria strigosa, Meandrina meandrites, Montastraea cavernosa, Porites astreoides, Porites porites) and is found in the Caribbean. Very little is known about the species in this genus.
G. cylindrus was isolated from within the gastrodermal cells of the mesenterial filaments of the coral. Only the oocysts and released sporozoites have been described. The parasites were isolated from bleached coral but their role if any in this sign is not known.