Infections of Unicauda clavicauda (Kudo, 1934) (Myxozoa) in the skin of Notropis hudsonius (Cyprinidae) from Montana, with a synopsis of the genus Unicauda Davis, 1944.

Infections of Unicauda clavicauda (Kudo, 1920) Davis, 1944 (Myxozoa) are described from Notropis hudsonius (Clinton) in Montana. Plasmodia form beneath scales of the body and produced spores within a loosely-defined matrix. Fixed spores are oval in front view, 11-14 microm long and 9-10.5 microm wide, and contain a posterior appendage that is up to 26 microm long. The polar capsules are 4-6 microm long and 2.5-4 microm wide. The study represents the first report of U. clavicauda since the original species description and a new host and geographical record. The taxonomic history of Unicauda Davis, 1944 is summarised and it is concluded the following 10 species are valid members of the genus: U. aristichthydis Zhao et Ma, 1995, U. brachyura (Ward, 1919), U. caudatus (Gogebashvili, 1965), U. clavicauda, U. crassicauda (Kudo, 1934), U lumae Rahemo, 1976, U. macrura (Gurley, 1893), U. magna Minchew, 1981, U. pelteobagrus Ma, 1998, and U. wuhanensis Xiao et Chen, 1993. All of these species have circular, subcircular, or oval spores in frontal view and all parasitise fish of the superorder Ostariophysi. As a group they are known from temperate freshwater locations in North America, Europe and Asia. A list of 16 species described or transferred to Unicauda at one time or another, but not recognised as members of the genus in the present study, is provided.