Cirripedia
Most parasites are really, really small. Especially the ones that mess with brains - they tend to be able to fit in them. But not all parasites that can do some fun jedi mind tricks are so itsy-bitsy. Take, for example, the Rhizocephalans - the parasitic barnacles.
Yes, I did just say parasitic barnacle. Although you probably wouldn't recognize it as a barnacle when it's an adult. The adult parasites look like a sac where a female crab would have eggs. It's classified as a barnacle, however, due to its larval forms, specifically the cypris larvae (left), which neatly place it in the class…