Siren

The siren is a creature that resembles a humanoid on its upper body and a fish on the lower half. They are hideous creatures that lure sailors into drowning themselves so the sirens can feast upon them.
They can vary greatly, some have the ability to shift the tone of their upper body which is where the typical depiction of a mermaid comes from, some can sing a song so hypnotizing it causes all to obey, some can even glide in the air giving them a more aggressive approach to catching prey.
They can live up to a century, but most die young, they are fertile since birth and only lay their eggs in the carcasses of sailors they have drowned. Their eggs are treated as a delicacy by nobles, however unknown to anyone but the poor that harvest them is that they are taken from rotten carcasses.