On the identity and nomenclature of <i>Paracanthonchus caecus</i> (Bastian, 1865), with a redefinition of the genus <i>Paracanthonchus Micoletzky</i> (Nematoda, Cyatholaimidae)

A historical review of the systematics of Paracanthonchus caecus (Bastian, 1865) and a comparison of specimens from different localities show that this &ldquo;species&rdquo; in fact comprises four distinct species. Paracanthonchus caecus Micoletzky, 1924 nec P. caecus (Bastian, 1865) is designated as the valid type species of the genus Paracanthonchus. P. heterodontus (Schulz, 1932) and P. thaumasius (Schulz, 1932) are re-established. P. caecm sensu Gerlach 1965 is considered as a distinct species: P. gerlachi sp.n. P. canadensis sp.n. is described and is very close to P. caecus Micoletzky, 1924. The subspecies P. caecus opthalmophorus (Steiner, 1921), different from the typical caecus by the presence of ocelli, is considered as a different species; we therefore propose P.ophthalmophorus (Steiner, 1921) stat.n. The genus Paracanthonchus is redefined