Sirens--- the beautiful, the terrifying.
Vicious, but, seemingly opportunistic creatures who lured sailors to their deaths by the sound of their captivating songs. Whether the stories of these creatures were a result of surviving sailors attempting to explain their near-miss in an effort to divert the fault of their shipwreck from their hands, or whether as a warning for those leaving to ensure their fidelity to the women they left behind, is unclear...
Considered the daughters of Achelous(river god), and though they have been blamed for the death of many sailors, they were not, however, sea deities. They have sometimes been called Muses of the lower world, their sad song causing the body and soul of those sailors who hear them to fall into a fatal lethargy.
In early myths, Sirens were the combined form of birds and women. Sometimes with a large female head, their bodies covered in bird feathers, their feet...scaled. Later myths show them as female figures with the legs of birds, though no wings, playing musical instruments---usually a harp.
There are a couple of specific myths involving Sirens where those fated to die, survived. One is of Jason, in Argonautica---Chiron (respected Centaur and oracle), divined that Jason would need Orpheus (legendary Greek musician) on his journey. When they passed the Sirens and the songs started, Orpheus pulled out his lyre and played a melody that drowned out the sound of their song, allowing Jason and his Argonauts to continue home from their quest for the golden fleece.
Odysseus' myth is probably the most well-known, especially to any High Schooler forced to endure The Odyssey (though I found it MUCH easier to digest than The Iliad).
Heeding Circe's (daughter of the sun god, Helios) warning, Odysseus had his sailor's plug their ears with beeswax, ensuring the Sirens would have no power over their fate. Curious, though, as to the sound of their song, Odysseus had his men strap him to the main mast---sans protective beeswax---and commanded they not untie him, no matter how much he begged or ordered them to do so. There he remained until their vessel passed out of earshot of the Sirens, suffering the pull of their song, but unable heed its call.
It was said that the Sirens were fated to die if someone heard their melodies, but escaped unharmed. And, when Odysseus passed, the Sirens, purportedly, flung themselves into the water.
A Song More Fair
A song more fair than night's beauty,
soft melodies ringing,
with cold waters mingling.
Yearning to bring lost souls closer,
fragile life protecting.
Heed warnings of those gone before,
calm waters beginning,
sweet music, your ending.