Nematoda (Nematode Worms)
Class: Chromadorea
Order: Araeolaimida
–No subordinate taxa
Order: Chromadorida
–No subordinate taxa
Order: Desmodorida
–No subordinate taxa
Order: Desmoscolecida
–No subordinate taxa
Order: Monhysterida
–No subordinate taxa
Order: Plectida
–No subordinate taxa
Order: Rhabditida
Family: Heligmonellidae
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
| Hassalstrongylus argentinus | (Freitas, Lent and Almeida, 1937) | - | (rediscovered) | Argentina | Rediscovered | Access |
| Hassalstrongylus dollfusi | (Díaz-Ungría, 1963) | (rediscovered) | Argentina | Rediscovered | Access | |
| Hassalstrongylus mazzai | (Freitas, Lent and Almeida, 1937) | - | (rediscovered) | Argentina | Rediscovered | Access |
incertae sedis: Ascaridoidea
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
| ?Ascaridoidea sp. nov. 'Steller's Sea Cow' | - | 1751 or before | Commander Islands, Bering Sea | Extinct | Access |
Class: Enoplea
Subclass: Dorylaimia
Order: Dorylaimida
–No subordinate taxa
Order: Marimermithida
–No subordinate taxa
Order: Mermithida
–No subordinate taxa
Order: Trichinellida
–No subordinate taxa
Subclass: Enoplia
Order: Enoplida
–No subordinate taxa
Order: Triplonchida
–No subordinate taxa
incertae sedis: Ichnospecies
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
| Agamofilaria oxyura | Schmidt et al., 1992 | - | Late Pleistocene-Holocene border | Arizona, USA | Extinct | Access |
| Alaichnus kabuverdiensis | Mayoral et al., 2018 | - | Late Pleistocene | Santiago, Cape Verde Islands | Extinct | Access |
| Archeococcidia antiquus | Schmidt et al., 1992 | - | Late Pleistocene-Holocene border | Arizona, USA | Extinct | Access |
| Archeococcidia nothrotheriopsae | Schmidt et al., 1992 | - | Late Pleistocene-Holocene border | Arizona, USA | Extinct | Access |
| Rhizocorallium jenense versum | Mayoral et al., 2018 | - | Late Pleistocene | Santiago, Cape Verde Islands | Extinct | Access |
| Strongyloides shastensis | Schmidt et al., 1992 | - | Late Pleistocene-Holocene border | Arizona, USA | Extinct | Access |