Together, the pearlfish and sea cucumber resemble some kind of a loaf, perhaps with asparagus sticking out. That's the pearlfish, which resides in the anal cavity of the sea cucumber to stay safe from predators. Although hiding from predators inside a sea cucumber presents an obvious benefit for a pearlfish, it isn't known whether the sea cucumber benefits from this relationship. Either way, the pearlfish usually isn't alone in there; a sea cucumber can actually house several fish at a time!
4. Portuguese man-of-war