Do sharks have parasites?
Everything has parasites, well, nearly everything. Parasites exist on nearly every organism and in nearly every environment. A parasite is (loosely defined) any organism that takes food or derives a benefit from another organism. The Remora is a type of fish that attaches to sharks and derives a benefit by cleaning the shark of parasites (copepods) that live and grow on the outside of the shark. The copepods often cause blindness in the shark and are often found inside the mouth and in the gills. Internally sharks have tapeworms and round worms. A tapeworm is long and flat like a long piece of tape. Round worms are round like an earthworm.
Yes. When I was in graduate school, my office mate was a guy working for his master's degree on the tapeworms of sharks. They're quite spectacular. Here's a collage of six of them that I collected from Google Images. These are colorized scanning electron micrographs of their scolices, the small end at which they attach to the host intestine (which most people probably would mistake for a head). The colors, of course, aren't biological-just fanciful embellishments by the people who processed the photos. Several or all of these photos are for sale on the web.