Hyptiasmus arcuatus (Brandes, 1892 of Stossich, 1902)— Type species

Syn. H. coelonodus Witenberg, 1923

Type host. Probably the ferruginous duck, Aythya nyroca (Güldenstädt) (Syn. Nyroca clangula [Linnaeus], but Nyroca Fleming is now a synonym of Aythya Boie) ( Anseriformes: Anatidae).

Type locality. Germany; specific type locality unknown.

Additional hosts. Smew, Mergellus albellus (Linnaeus) ( Anseriformes: Anatidae)— Yamaguti (1934); species of Anas Linnaeus, Anser Brisson, Bucephala Baird (Syn. Glaucionetta Stejneger), Clangula Leach, Fulica Linnaeus, Melanitta Boie (Syn. Oidemia Fleming), Somateria Leach and Turdus Linnaeus—Yamaguti (1971); common or red-headed pochard, Aythya ferina (Linnaeus) (Syn. Fuligula ferina Linnaeus) ( Anseriformes: Anatidae)— Witenberg (1923). NHMUK on-line Host-Parasite Database lists 13 avian host species for H. arcuatus and the red-head pochard or red-headed duck, Fuligula ferina (Linnaeus) ( Anseriformes: Anatidae), as a host for H. coelonodus (see Chertkova et al. 1994).

Additional localities. Sizuoka Prefecture—Yamaguti (1934); Europe, Japan, Salvador (Brazil) and Siberia— Yamaguit (1971). NHMUK on-line Host-Parasite Database lists 8 localities and 16 references for H. arcuatus and the “European USSR (CIS)” as a locality for H. coelonodus (see Chertkova et al. 1994).

Previously proposed synonyms. Hyptiasmus laevigatus Kossack, 1911, H. tumidus Kossack, 1911, Hyptiasmus oculeus (Kossack, 1911), H. magnus Johnston, 1917, H. coelonodus, Transcoelum oculeum (Kossack, 1911) (= Hyptiasmus oculeus), and Transcoelum sigillum Witenberg, 1923 (= Hyptiasmus sigillum [Witenberg, 1923] n. comb.)— Joyeux & Baer (1927); Hyptiasmus laevigatus, Hyptiasmus tumidus, Hyptiasmus coelonodus, Hyptiasmus theodori Witenberg, 1928 — Dubois (1959).

Remarks. This species was originally erected without description or illustrations as Monostomum arcuatum Brandes, 1892 . Stossich (1902) considered Monostomum arcuatum to be a nomen nudum and therefore provided a minimal description with an illustration, and transferred this species to Cyclocoelum . Kossack (1911) transferred it to Hyptiasmus, and redescribed and reillustrated the species from specimens deposited in the Berlin Museum (Berliner Sammlung, No. 2586). Hyptiasmus coelonodus also was originally described from a species of Aythya (Anatidae) from Europe, and differs from H. arcuatus by having a somewhat larger intertesticular space (1,500 long, 9% of body length compared to about 700, 6%); however, these values are within the normal ranges in species of cyclocoelids and H. coelonodus otherwise cannot be distinguished from H. arcuatus; therefore, it is placed in synonymy with H. arcuatus . No oral or ventral sucker described—Stossich (1902); Kossack (1911); Witenberg (1923, 1926); Bashkirova (1950).