The Sirens of Greek mythology are sometimes portrayed in later folklore as fully aquatic and mermaid-like; the fact that in Spanish, French, Italian, Polish, Romanian, Portuguese and Filipino the word for mermaid is respectively Sirena, Sirène, Sirena, Syrena, Sirenă, Sereia and Sirena and that in biology the Sirenia comprise an order of fully aquatic mammals that includes the dugong and manatee, add to the visual confusion, so that Sirens are even represented as mermaids. However, "the sirens, though they sing to mariners, are not sea-maidens," Harrison had cautioned; "they dwell on an island in a flowery meadow." In the Philippine mythology, the Sirena is a mythological aquatic creature with the head and torso of human female and the tail of a fish. The male version of a Sirena is called a Sireno. Sometimes it is also paired with Siyokoy (see below). The Sirena is an engkanto which is classified as one of the Bantay Tubig or the guardians of water. In addition to the Sirena, other examples of Bantay Tubig are Sireno, Siyokoy, Kataw and Ugkoy. Bantay Tubig are part fish, part human water-dwelling engkantos which are the Filipino
The Filipinos in the Medieval Period said that it started somewhere in a place now called "Tandang Sora". There was a fisherman that was attracted to a tilapia, a kind of fish that is abundant in tropical countries. This fisherman was so sexually attracted to the tilapia and begun to masturbate for it. He was not contented and raped the fish. After 4 months, the fisherman was shocked when he saw that this tilapia was pregnant. He could not believe as for what he saw that night, it was also the very night that the fish will have her delivery. The fish gave birth of a half human, half fish creature. As the fisherman knew that this creature is so valuable, he then named it "GEM". They also said that when a "Sirena" get a hold of a stone called "DARNA'S STONE" this creature can be seen as a whole human.
Dugongs, sea turtles, and small cetaceans such as dolphins usually accompany the Sirena.