“A shade-loving snail has been invaded by worms. These parasites take over the snail’s brain, and push into his tentacles, transforming them into swollen, colorful, pulsating targets…”
This parasite is apparently called Leucochloridium paradoxum.
There are many other “mind-controlling” parasites such as the Spinochordodes Tellinii which infect grasshoppers and forces them to drown themselves. The animal develops inside land-dwelling grasshoppers and crickets until the time comes for the worm to transform into an aquatic adult. Somehow mature hairworms brainwash their hosts into behaving in way they never usually would – causing them to seek out and plunge into water.
Once in the water the mature hairworms – which are three to four times longer that their hosts when extended – emerge and swim away to find a mate, leaving their host dead or dying in the water.