Intraspecific variation in Diplophallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae) from avocets and stilts (Recurvirostridae) in North America

Diplopallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae), hitherto recorded from avocets Recurvirostra avosetta L. and stilts Himantopus himantopus (L.) (Recurvirostridae) in Europe, Asia and Africa, is reported for the first time as a parasite of Recurvirostra americana Gmelin, 1788 and Himantopus mexicanus (Milller, 1776) in the Pacific, Central and Mississippi migratory flyways of North America. D. polymorphus is redescribed, as it shows great intraspecific variation in the number (20–25) and size (0.087-0.122 mm) of the rostellar hooks and in the position of the cirrus-sac and relation of the external seminal vesicle to the longitudinal excretory vessels. It is found that the intraspecific variations are neither related to host nor to locality of the host. The possible synonymy of D. polymorphus with D. colli Ahern & Schmidt, 1976 and with Himantocestus blanksoni Ukoli, 1965 is discussed.