Cel was the Etruscan goddess of the earth. On the Etruscan calendar, the month of Celi (September) is likely named for Her Greek counterpart is Gaia and her Roman is Tellus. In Etruscan mythology, Cel was the mother of the Giants.
A Siren isn't really a sea monster but sailors have told tales of these beautiful women that sing to you and seduce you into their trap of bloodlust. They are said to eat the sailors alive or drowned them deep in the ocean.