Acanthocephala, including the descriptions of two new species of Mediorhynchus (Gigantorhynchidae) from birds from Paraguay, South America

Mediorhynchus emberizae (Rudolphi, 1819), M. micracanthus (Rudolphi, 1819) and M. papillosus, Van Cleave, 1916 and two new species M. amini from Myiarchus ferox (Gmelin, 1798) and M. ayeri from Pitangus sulfuratus Linneaus, 1776, Agelaioides badius (Vieillot, 1819), Arremon flavirostris (Swainson, 1830), Furnarius cristatus Burmeister, 1888, F. rufus (Gmelin, 1788) and Zonotrichia capensis (Statius Mueller, 1776) are reported from Paraguay for the first time. An additional putative new species could not be described fully because of insufficient material. A more complete description of M. micracanthus is given. The new species are distinguished from congenerics principally by proboscis armature and hook size but also by body size, lemnisci length and testis size. Acantho-cephalans, Gigantorhynchidae from bird hosts, Mediorhynchus spp. that could not be fully identified, are listed.