With respect to Plasmodium and related genera of blood parasites, major clades are associated with shifts into different families of dipteran vectors, and the Plasmodium species of birds and squamate reptiles show evidence of repeated switching back and forth (Martinsen et al., 2008) . Major lineages within the blood fluke genus Schistosoma are defined by acquisition of different genera of even families of snail intermediate hosts, by host switching (Morgan et al., 2003) . Long-range host shifts involving acquisition of both new snail and vertebrate hosts appear to have occurred during the history of schistosomes (Brant and Loker, 2005) . Zietara and Lumme (2002) note that as many as 20,000 species of the monogenean genus Gyrodactylus may exist, and note that in a study of one subgenus (Limnonephrotus) that several host switch events were statistically confirmed, including into new host families, supporting the idea that host switching is a means to drive innovation and adaptive radiation in these ectoparasites.