One way to look at parasites is as generalists or specialists. Generalists are non-host specific and while some infect a group of related hosts, others may infect completely unrelated hosts. Specialists infect only one species of host. This strange-looking trematode with wing-like expansions on the anterior end is an intestinal parasite of the osprey, Pandion haliaetus. The osprey is so highly evolved that it is the only species in its own family, Pandionidae. Perhaps because of its evolutionary isolation, the osprey has an unusual number of helminth specialists, and because its diet is 99% fish, almost all of them probably use fish as an intermediate host.
Contributed by Mike Kinsella.