A Mermaid is a fictitious or mythical half-human Ocean or Sea creature with the head and trunk of a woman and the tail of a fish. Mermaids are seen as virgins because they haven't got the lower part of a human body that they'd need to have Sex.
In the animal planet TV show about mermaids (Which is evidence the Animal Planet channel is ultimately to fall the same fate History Channel has, it already kind of has.), there are these strange creatures that apparently communicated with dolphins and their main problem was megalodons that would eat them. Mermaids are a fantasy though and don't actually exist and never did, although it is fun to imagine a battle between mermaids and a megalodon, of course, the megalodon wins the battle.
I completely missed the disgraceful hokum the Animal Planet channel aired last week, Mermaids: The Body Found, a completely fictional pseudodocumentary dressed up as reality that claims mermaids exist. You can watch it now, though, until Animal Planet takes it down. (PZ Myers)