Phylum: Nematoda (Nematode Worms or Roundworms)
"Nematodes are the most numerous multi-cellular animals on earth, with more than 80,000 species described, including about 2,500 being plant parasitic. Nematodes are elongated, non-segmented microscopic eel-like roundworms that can be beneficial or non-beneficial. They live in soil and plant root tissues. Most are considered beneficial to the soil, as they contribute to the decomposition of organic matter. Only a small percentage of nematode species are parasitic and harmful to crops, causing damage to plants by feeding on roots. Some nematodes attack soil-living insect pests and can be used as biocontrol organisms"
Source: https://treefruit.wsu.edu/web-article/nematodes/
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 & Almeida, 1937) | - | (rediscovered) | Argentina | Rediscovered | Access |
| Hassalstrongylus dollfusi | (Díaz-Ungría, 1963) | Dollfus's hassalstrongylus nematode worm | (rediscovered) | Argentina | Rediscovered | Access |
| Hassalstrongylus mazzai | (Freitas, Lent & 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
Appendix 1: Ichnotaxa
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Taxon Profile |
| Agamofilaria oxyura | Schmidt et al., 1992 | - | Late Pleistocene or Holocene | Arizona, USA | Access |
| Archeococcidia antiquus | Schmidt et al., 1992 | - | Late Pleistocene or Holocene | Arizona, USA | Access |
| Archeococcidia nothrotheriopsae | Schmidt et al., 1992 | - | Late Pleistocene or Holocene | Arizona, USA | Access |
| Strongyloides shastensis | Schmidt et al., 1992 | - | Late Pleistocene or Holocene | Arizona, USA | Access |
Statistics
| Conservation status | Number of taxa (in percentage) |
| Extinct | 1 (25%) |
| Missing | 0 |
| Extinct in the Wild | 0 |
| Possibly Extinct in the Wild | 0 |
| Globally Rediscovered | 3 (75%) |
| Rediscovered in the Wild | 0 |
| Reintroduced | 0 |
| Hypothetical | 0 |
| Invalid | 0 |
| Erroneously listed | 0 |
| Uncertain status | 0 |
| Total | 4 |