Anguillicoloides novaezelandiae

Anguillicoloides novaezelandiae is a parasitic nematode worm that lives in the swimbladders of eels (Anguilla spp.), particularly Anguilla australiensis, Anguilla anguilla and Anguilla dieffenbachii. Specimens have been located in Italy (where it is thought to have been introduced) and New Zealand (where it is a native species). The species is most similar to A. Australiensis. However, it differs from the latter species in the shape of the head end which is bulbously inflated, almost spherical, and followed by a marked neck constriction in A. Australiensis, whereas it is only slightly expanded in A. novaezelandiae. Also, the anterior ovary in A. australiensis females extends anteriorly to about the mid-length of the oesophagus, while it does not reach the end of the oesophagus in A. novaezelandiae. Both species differ in size and form. While the body of A. australiensis is long (30 millimetres (1.2 in) to 40 millimetres (1.6 in) in males and 60 millimetres (2.4 in) to 70 millimetres (2.8 in) in gravid females) and relatively slender (at most 1.5 millimetres (0.059 in) in gravid females), that of A. novaezelandiae is much shorter (between 6 and 15 millimetres (0.24 and 0.59 in) in males and between 10 and 31 millimetres (0.39 and 1.22 in) in gravid females) and wider (up to 3 millimetres (0.12 in) in gravid females). The shape of the posterior end of the female body is different in these two species.

The state of being colonized by Anguillicola nematodes is termed anguillicolosis.