H. laevigatus Kossack, 1911

Type host. Tufted duck, Aythya fuligula (Linnaeus) (Syns. Anas fuligula Linnaeus; Fuligula fuligula [Linnaeus]) ( Anseriformes: Anatidae).

Type locality. Germany; specific type locality unknown.

Additional hosts. Velvet scoter, Melanitta fusca (Linnaeus) (Syn. Oidemia fusca Linnaeus); common scoter, Melanitta nigra (Linnaeus) (Syn. Oidemia nigra Linnaeus); common eider, Somateria mollissima (Linnaeus); long-tailed duck, Clangula hyemalis (Linnaeus) (Syn. Nyroca hyemalis [Linnaeus]) ( Anseriformes: Anatidae); and species of Anas Linnaeus and Anser Brisson—Kossack (1911); Yamaguti (1971); ferruginous duck, Aythya nyroca (Güldenstädt) ( Anseriformes: Anatidae)— NHMUK on-line Host-Parasite Database.

Additional localities. Europe, Republic of Kazakhstan and Siberia—Yamaguti (1971). Bulgaria—NHMUK on-line Host-Parasite Database.

Previously proposed synonyms. Hyptiasmus tumidus Kossack, 1911; H. coelonodus Witenberg, 1923 — Bashkirova (1950).

Remarks. No oral or ventral sucker described—Kossack (1911); Witenberg (1923, 1926) and Bashkirova (1950).