1) Sporozoan zygotes 
The resistant stage of the life cycle of coccidial parasites (present in a cat's intestinal tract, also found in the liver and other organs).
A part of the sporogony phase of protozoa which occurs after macro-gametes have been fertilised by micro-gametes in the intermediate host. The subsequent multiplication of cells produces an oocyst, each cell then becoming a sporozoite which is subsequently injected into the final host.
persistent reproductive spores of Cryptosporidium; excreted by infected animals and spread in unfiltered water; highly resistant to chlorine but destroyed by heat or ozone