1. Larvae ........ Go to: 4 & 5
2. Ova .......... Go to: 6, 7, & 8
3. Adult Worms .......... Go to: 20, 21, 22, & 23

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

6. Ova in feces ........ Go to: 9 & 10
7. Ova in urine ........ Capillaria sp. (Go to: Capillarid Ova section)
8. Ova in sputum, or nasal discharge ........ Capillaria sp. (Go to: Capillarid Ova section)

9. Ova in feces with bipolar plugs ........ Go to: 11 & 12
10. Ova in feces without bipolar plugs ........ Go to: 13 & 14

11. Ova oval, shell smooth in cross-section and smooth on surface ........ Trichuris vulpis
12. Ova ellipsoid, shell faintly striated in cross-section and delicately pitted surface or delicate netlike surface ........ Capillaria sp. (Go to: Capillarid Ova section)

13. Ova with a rough coat around the shell ........ Toxocara canis
14. Ova with a smooth shell .......... Go to: 15 & 16

15. Ova ellipsoid, with morula stage filling all of the shell ........ Hookworm (Ancylostoma sp. or Uncinaria sp.)
16. Ova oval, with single-cell stage pulled away from the interior shell wall ........ Toxascaris leonina

Capillarid Ova*
17. Ova in feces, sputum or nasal discharge; ellipsoidal, bipolar plugs, shell faintly striated in cross-section, with a delicately pitted surface ........ Capillaria (Eucoleus) boehmi
18. Ova in feces, sputum or nasal discharge; ellipsoidal, bipolar plugs, shell faintly striated in cross-section and has a delicate netlike surface ........ Capillaria (Eucoleus) aerophilus
19. Ova in urine; ellipsoidal, bipolar plugs, shell rough in cross section, with a thick bead-like or mesh-like surface ........ Capillaria (Pearsonema) plica

* See: "Trichuris and Other Trichenelloid Nematodes of Dogs and Cats in the United States." Compendium on Continuing Education for the Practicing Veterinarian. May 1991. 13 (5): 769-778.

20. Adult nematode found in a Subcutaneous nodule ........ Dracunculus insignis
21. Adult nematode found in Abdominal cavity during a spay ........ Dioctophyme renale
22. Adult worm in feces .......... Go to: 24 & 25
23. Adult nematode in vomitus .......... Go to: 26 & 27

24. Body generally wrinkles. Anterior end possesses a rounded proboscis with hooks ........ Macracanthorhynchus ingens*
Note: Macracanthorhynchus ingens is an Acanthocephalan (thorny-headed worm ) NOT a Nematode
25. Body generally smooth. Anterior end is rounded with large lips and cervical alae ........ Go to: 28

27. Anterior end is bunt with a cuticular collar ........ Physaloptera sp.
26. Anterior end is rounded with large lips and cervical alae ........ Go to: 28

28. The tail of the male worm is finger-like ........ Toxocara canis
29. The tail of the male worm is triangular and NOT finger-like .......... Toxascaris leonina