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. novaeze