Description of Sarcocystis falcatula stiles, 1893, a parasite of birds and opossums.

Sarcocystis falcatula Stiles, 1893 is re-described. Intermediate hosts of the parasite which was earlier described as Sarcocystis debonei Vogelsang, 1929 are species of passeriform, psittaciform, and columbiform birds. In these birds, muscle zoites are 6.88 X 2.19 (4.8-8.4 X 1.2-3.6) micron and are enclosed in a cyst wall with regular protrusions, 1-5 micron long. The convoluted primary wall has multiple thin areas in the osmiophilic layer. Microtubules originate in the ground substance and extend to the tips of the protrusions. The only known definitive host is the opossum, Didelphis virginiana; rats, cats, a dog, and a ferret could not be infected from muscle cysts. Sporocysts from opossums infected from five different infected avian sources measure 11.2 X 7.4 (9.6-12.0 X 6.0-8.4) micron.