The collection of horsehair worms in the Zoological Museum of the Centrum für Naturkunde (CeNak) of the University of Hamburg has been revised. All specimens have been investigated by Scanning Electron Microscopy (SEM). A total of 173 specimens from 135 catalogue entries is present in the collection, these represent 39 species from 10 genera (Gordius, Chordodes, Paragordius, Parachordodes, Gordionus, Acutogordius, Beatogordius, Paragordionus, Pseudochordodes, Nectonema). Previous revisions of the Nematomorpha material have been done in 1893 by Römer and in 1935 by Heinze. A number of species could not be determined to species level, either because characters were not preserved well enough or because observed characters did not fit available species descriptions. This does account in particular for the genus Gordius, where diagnostic characters are few and great uncertainties exist concerning the status of certain species. Therefore, within this genus, many records were only determined as Gordius sp., including some specimens that had previously been determined to species level. One new species is described from the material of the collection. This species is named Chordodes jelkae sp. n. and it is characterized by the presence of an apical tuft of bristles on simple areoles in combination with the absence of thorn areoles. The holotype of Chordodes pilosus Möbius, 1855 was reinvestigated, and its species identity cannot be determined unambiguously. Therefore the name Chordodes pilosus is considered a nomen dubium.
