File this one under "almost extinct." With a face that only a mother could love, the frilled shark (named for its six pairs of frill-like gills) is quite possibly the ugliest, strangest and most frightening monster on this list [sources: SETFIA, Chappell]. This bizarre and menacing creature is not, in other words, the type of shark one might find dancing behind Katy Perry during a Super Bowl halftime show.
The frilled shark kind of looks like an ugly version of an electric eel. Its 5-foot (1.5-meter) frame slithers around with the help of a few small fins and strikes a bowel movement-inducing fear in the heart of any human who crosses its path, with a set of 300 razor-sharp teeth laid out in 25 rows. The shark has been called a "living fossil" thanks to those primitive features and an origin that traces back roughly 80 million years [sources: SETFIA, Chappell].
Until recently, it may have been safe to believe that this beast had gone the way of the megalodon. That's until a couple of Australian fishermen happened to inadvertently scoop one up in their net in January 2015 [source: Chappell]. It's one of a few known modern encounters with the beast, at least by anyone who's lived to tell about it.