To humans, these are Very Scary Death Eels. Far worse than arse eels. They will make their own gills between our hoo-man ribcages. If management get wind, we're fucked!
Hmm... After reading the article it seems the shark was more a target of opportunity rather than this being a regular parasitic relationship between two species. Which is only very small comfort. Ew.
Top creepy parasite for me is still the fish-tongue parasite, although I'm sure someone who knows more about what insects get up to will be along shortly to creepy me out even worse.
^The fungus that attacks the ant is called Cordyceps. It is related to one that grows on caterpillars and is used in Chinese Medicine. (Dong Chong Xia Cao - lit. "Winter Bug, Summer Herb"). Works great for lung problems.
Is it fucked that when I clicked on the heartworms link, the first thing I noticed was that the image on the wiki page looked like it had a smiling cow in the middle of it with its head at a 3/4 turn to the camera? :O