A redescription of Eustrongylides tubifex (Nitzsch 1819) Jägerskiöld 1909 (Nematoda: Dioctophymatidae) from mallards (Anas platyrhynchos).

Eustrongylides tubifex (Nitzsch 1819) Jägerskiöld 1909 is redescribed from six male and 10 female adult specimens from experimental infections in mallards (Anas platyrhynchos). Our redescription is compared with that of Jägerskiöld (1909) and those of the Russian investigators Kontrimavichus and Bakhmeteva (1960) and Karmanova (1968). Our redescription differs in the ranges of total body length, esophageal length, maximum width, spicule length and vagina length. The cuticular fringe and inner rim of small papillae of the male bursa are shown to be definitive species characters. A key to the species of Eustrongylides is included.