| 1. | a. | No cephalic capsule and stoma without mandibles but with teeth or unarmed; caudal glands absent or in tail or extending precaudally | 2 |
| b. | Cephalic capsule present and stoma with solid mandibles with unguiform anterior end (Fig. 9.4 J); teeth shorter than mandibles; one tubular precloacal supplement in male; caudal glands extending precaudally. | Enoplina Family: Enoplidae Enoploides |
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| 2. | a. | Stoma very small, almost nonexistent. | 3 |
| b. | Stoma larger, armed with teeth or unarmed. | 5 | |
| 3. | a. | Body not extremely narrowing anteriorly; caudal glands absent | 4 |
| b. | Body very thin anteriorly, at low magnification head region difficult to differentiate from tail region; caudal glands present | Ironina Family: Oxystomatidae |
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| 4. | a. | Anterior sensilla arranged in two circlets and papilliform; males monorchic. | Alaimina Family: Alaimidae |
| b. | Only six outer labial setae visible; males diorchic. | Family Andrassyiidae Malakhovia |
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| 5. | a. | Stoma not elongated, armed or unarmed | 6 |
| b. | Stoma elongated, anteriorly with three well-developed eversible hamulate teeth (Fig. 9.4 K) | Ironina Family: Ironidae Ironus |
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| 6. | a. | Stoma subdivided or not, armed with teeth. | 7 |
| b. | Stoma large spacious and toothless. | Enoplina Family: Anoplostomidae Anoplostoma |
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| 7. | a. | Stoma subdivided, teeth present. | 8 |
| b. | Stoma not subdivided or with different chambers; teeth large, hollow, can be unequal (Fig. 9.4 P) | Family: Oncholaimidae | |
| 8. | a. | Stoma subdivided in two unequal parts, with three teeth and largest tooth ventrosublateral; male exceptionally without stoma | Family: Enchelidiidae |
| b. | Stoma with several chambers, armed with teeth or cuticular projections; six outer labial setae longer than four cephalic setae | Tripyloidina Family: Tripyloididae Tripyloides |