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 in blood .......... Dirofilaria immitis
5. Larvae in feces .......... Strongyloides stercoralis


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

8. Eggs or cysts with smooth non-ornate shells. ...... Go to: 10, 11, & 12
9. Eggs or cysts with ornate (plugs, operculum, striations, rough) shells.
                                                                                .......... Go to: 15 & 16


10. Eggs or cysts with a single cell embryo. .......... Go to: 13 & 14
11. Morulated egg. .......... Hook-worm egg
12. Egg with a developed larval trematode.
                                              .......... Heterobilharzia americana


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

15. Spherical to oval eggs with striated or rough shell.
                                                                                .......... Go to: 17 & 18
16. Oval to Elongate eggs with operculum or bi-polar plugs.
                                                                                .......... Go to: 19 & 20


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


19. Eggs with bipolar plugs. .......... Go to: 21 & 22
20. Eggs with a single operculum. .......... Go to: 23 & 24

21. Bi-polar plugs with a smooth shell surface.
                                                          ....... Trichuris vulpis
22. Bi-polar plugs with fine pits on the shell surface.
                                                                  .......... Capillaria boehmi


23. Large egg with a rim around the operculum.
                                                      .......... Paragonimus kellicotti
24. Smaller egg without a rim around the operculum.
                                                                      .......... Spirometra sp.