Sirens and mermaids in English are two different creatures, but one in the same in Italian. Both belong to the menagerie of mythological females who lure men to their doom. In the case of the siren it is her voice that holds the fatal power, with the mermaid her sensuality.

Etruscan Mermaid 5th Century BC

That said, the pagan mermaids like those depicted by the Etruscans, appear to have no negative connotations, implying a more balanced sexuality than in this opinion by the aptly named Jesuit Cornelius Lapide, who said of Woman, “her glance is that of the fabled basilisk, her voice a siren’s voice—with her voice she enchants, with her beauty she deprives of reason—voice and sight alike deal destruction and death.”
This picture was designed for a cover of a book called ‘Se il Pesce avesse le cosce’ which roughly translates as ‘If a fish only had thighs’. It was a book of erotic recipes.