Date of this Version
Members of the family Rhopaliidae Looss, 1899 include digenetic trematodes that are parasites of marsupials in the Nearctic and Neotropical regions. These forms are characterized by having two anteriorly directed proboscides armed with spines and situated bilaterally relative to the oral sucker. The family was first established by Looss (1899) as the Rhopaliadae. Braun (1901b) incorrectly spelled the subfamily name as Rhopaliadinae. These trematodes were further studied and redescribed by Fuhrmann (1928) and Bresslau (1932), while Pratt (1902) appears to have been the first to consider the group to be related to the schinostomes. Viana (1924) emended the spelling of the family name to Rhopaliidae, which Skrjabin (1948c) considered a synonym of the Rhopaliadae. The spelling Rhopaliasidae was used by Yamaguti (1958). Travassos et al. (1969) established the subfamily Rhopaliasinae, and Yamaguti (1971) synonymized the Rhopaliasidae with the Rhopaliidae. The name Rhopalias was established by Stiles & Hassall (1898) to replace Rhopalophorus Diesing, 1850, which was pre-occupied by Ropalophorus Westwood, 1840 (Hymenoptera), with Distomum coronation Rudolphi, 1819 as the type-species. Rhopalophorus is synonymous with Rhopalias Stiles & Hassall, 1898. Lutz (1895) used the name Rhopalocephalus, without citing a taxon authority, in conjunction with the species names R. coronatus (Rudolphi, 1819) and R. horridus (Diesing, 1850). Stiles & Hassall (1898) did not mention Rhopalocephalus and, presumably, were unaware of it. It does not appear to have been used by other authors. Although Rhopalocephala is the older name, Rhopalias is well established in the literature and we intend to petition the ICZN to declare Rhopalocepbalus a nomen oblitum. The primary distinguishing morphological character of Rhopalias is the possession of a pair of proboscides, armed with chitinous spines, which can be invaginated into a muscular pouch. The pouches open to the exterior on each side of the oral sucker. They are about 0.3 mm long, with protrusor and retractor muscle fibres. The number and arrangement of spines on the proboscides are diagnostic at species level. Among the species, the proboscides range from fairly short <0.26 mm) with 7-8 spines, in R. baculiler Braun, 1900, medium in length <0.32 mm) with many spines, in R. horridus (Diesing, 1850), or medium with ten spines in a dorsal and a ventral group of five spines each, in R. macracantbus Chandler, 1932 or, finally, very long <1.3mm) with ten spines each in R. coronatus (Rudolphi, 1819).