1. Nematode Larva with S-shaped tail spine
                                                            .......... Aelurostrongylus sp.
2. Helminth Egg or Protozoal Cyst .......... Go to: 4 & 5
3. Worms / Segments in feces / vomitus .......... Go to: Gross Worm Key


4. Large packet of 2 or more spherical eggs. ........ Dipylidium sp.
5. Single egg or cyst .......... Go to: 6 & 7


6. Eggs or cysts with smooth non-ornate shells. .......... Go to: 8 & 9
7. Eggs or cysts with ornate (operculum, striations, rough) shells.
                                                                            .......... Go to: 10 & 11


8. Small protozoan oocyst with thin shell with a single cell embryo.
                                                            .......... Cystoisospora sp.
9. Morulated egg. .......... Hookworm egg


10. Spherical to oval eggs with striated or rough shell.
                                                                            .......... Go to: 12 & 13
11. Oval eggs with an operculum. .......... Go to: 14 & 15


12. Small spherical egg w/ striated shell & embryo w/ hooklets.
                                                            .......... Taenia taeniaformis
13. Large round to oval egg w/ rough pitted shell & single cell embryo.
                                                            .......... Toxocara cati


14. Large egg with a rim around the operculum.
                                                          .......... Paragonimus kellicotti
15. Smaller egg without a rim around the operculum.
                                                            .......... Spirometra sp.