<i>Myxidium macrocheili</i> n. sp. (Cnidospora: Myxidiidae) from the Largescale Sucker <i>Catostomus macrocheilus</i> Girard, and a Synopsis of the <i>Myxidium</i> of North American Freshwater Vertebrates*

Abstract

SYNOPSIS. Myxidium macrocheili n. sp. is described from the gall bladder, bile and pancreatic ducts of Catostomus macrocheilus Girard (largescale sucker) in western Montana. This parasite is markedly host specific; the trophozoite is nonmotile, polysporous, spheroidal, elongated or irregular, often arched and rolled at the edges, and up to 2.5 mm in greatest length; the ecto‐ and endoplasm are distinct; the sporonts are disporoblastic. The bipolar spore is longitudinally striated, usually ellipsoidal in front view, slightly S‐shaped in side view, and averages 11.7 × 6.6 × 6.3 μ; the suture line and ridge are distinct; the polar filaments are coiled 4–6 times. An illustrated synopsis and a key of the 19 species and 10 unnamed forms of Myxidium of North American freshwater vertebrates are presented. At present members of the genus are known to infect fishes, amphibians and a single species of reptile on this continent.