DESCRIPTION OF MEDIORHYNCHUS-PAPILLOSUS (ACANTHOCEPHALA, GIGANTORHYNCHIDAE) FROM A COLORADO, USA, POPULATION, WITH A DISCUSSION OF MORPHOLOGY AND GEOGRAPHICAL VARIABILITY

The original description of Mediorhynchus papillosus Van Cleave, 1916 included misinterpretations of such taxonomically important structures as proboscis armature. The species was briefly redescribed from Asian material by Schmidt and Kuntz (1977) as well as by various Russian an d other workers before and after 1977. The present collection from Col orado provided important taxonomic information previously unreported o r erroneously interpreted. The first description of M. papillosus from North American specimens collected from a sage thrasher, Oreoscoptes montanus Baird, 1858, in Colorado, U.S.A., is presented with new featu res reported for the first time. A comprehensive comparison of the Nor th American, Asian, and Russian populations is presented and discussed . Mediorhynchus papillosus appears to be a geographically variable spe cies, particularly in size of proboscis and its armature, and relative space occupied by the neck and posterior proboscis. The geographicall y isolated Taiwanese population was markedly different from the Colora do population; the latter was more similar to others from various Sovi et republics, particularly the Ukraine. Distinctiveness of geographica l populations appears to be related to geographical restrictions, inte rmediate and definitive host specificity and distribution, and host fe eding behavior.