Gordionus maori (Nematomorpha: Gordiida), a new species of horsehair worm from New Zealand

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Only four species of freshwater Nematomorpha (Gordiida) and one undetermined Gordius sp. are known from New Zealand. During recent surveys in the South Island we discovered a new species belonging to the genus Gordionus, a genus new to New Zealand. Scanning electron microscopic observations of seven collected specimens revealed that the species is clearly morphologically distinct from all other members of the genus and is characterised by the presence of an extensive row of large bristles on the ventral side of the posterior end in males. This row is much larger than in any known Gordionus species. Analysis of the mitochondrial CO1 gene and of the nuclear 18S rRNA gene showed that the new Gordionus specimens form a monophyletic clade, but with partly extensive internal genetic difference. This indicates that cryptic species might be present, for although there are minor variations in cuticular areoles, other morphological characters indicate little difference between specimens.

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