1. Nematode Larva ........ Go to: 4 & 5
2. Helminth Egg or Protozoal Cyst .......... Go to: 6 & 7
3. Worms / Segments in feces / vomitus .......... Go to: Gross Worm Key


4. Larvae with S-shaped tail spine .......... Aelurostrongylus sp.
5. Larvae straight conical tail .......... Strongyloides stercoralis


6. Large packet of 2 or more spherical eggs. ........ Dipylidium sp.
7. Single egg or cyst .......... Go to: 8 & 9


8. Eggs or cysts with smooth non-ornate shells. .......... Go to: 10 & 11
9. Eggs or cysts with ornate (operculum, striations, rough) shells.
                                                                            .......... Go to: 14 & 15


10. Eggs or cysts with a single cell embryo. .......... Go to: 12 & 13
11. Morulated egg. .......... Hookworm egg

12. Large egg with thick smooth shell and internal prominent lipid layer.
                                                                .......... Toxascaris leonina
13. Small protozoan oocyst with thin shell. ........ Cystoisospora sp.


14. Spherical to oval eggs with striated or rough shell.
                                                                            .......... Go to: 16 & 17
15. Oval eggs with an operculum. .......... Go to: 18 & 19


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

18. Large egg with a rim around the operculum.
                                                          .......... Paragonimus kellicotti
19. Smaller egg without a rim around the operculum.
                                                            .......... Spirometra sp.