Cattiena fansipanis n. sp. (Nematoda: Rhigonematida: Carnoyidae) from a millipede (Myriapoda: Diplopoda: Spirobolida) in North Vietnam.

A new species of Cattiena Hunt & Spiridonov, 2001 from a diplopod (Spirobolida: Pseudospirobolellidae Brolemann) collected near Sa Pa, Lao Cai Province, Vietnam, is described. Females of Cattiena fansipanis n. sp. are closely related to females of two other known species of the genus, C. trachelomegali Hunt & Spiridonov, 2001 and C. trigoniuli Hunt & Spiridonov, 2001, but can be distinguished by the distinctly more anterior position of the vulva, abrupt constriction of the body at the vulval level, presence of two swollen portions of the oviducts, and longer body and tail. Males of new species differ by having a rounded cephalic region followed by 13-14 annules which are larger than those which follow them, a different size and shape of the spicules and gubernaculum, and body and tail length. Three size groups of juveniles were found in the host gut lumen, presumably representing second, third and fourth juvenile stages. The morphology of the juvenile stages is described.