The Siren Sisters (サイレンシスターズ?, Sairen Shisutāzu), Morphea (モルフィア?, Morufia), Minaton (ミナトン?, Minaton), and Kaidora (カイドラ?, Kaidora), are siren kaiju created by Hanna-Barbera that appeared in the 1978 The Godzilla Power Hour episode, The Island of Lost Ships.
After an ancient Greek island re-appears in the Earth dimension after 1,000 years, Captain Majors is hypnotically induced to bring the Calico there by a mysteriously beautiful singing. Upon arriving, the crew discovers that the island is the home of the Sirens, three deadly sisters from Greek mythology who entrance male sailors with their hypnotic singing, luring them to the island where they meet their doom. Although the leader of the Sirens, Morphea, initially seems to welcome the crew, they soon learn that they are to be kept on the island after it disappears at sunset by being turned to stone (an idea the Sirens possibly stole from another trio of deadly sisters from Greek mythology, the Gorgons). After the crew opens the doors to a chamber against the warnings of Morphea, they release a Chimera, a gigantic fire-breathing mythological monster that is a three-way cross between a lion, a goat, and a serpent. After Morphea exclaims that not even the Sirens can control the Chimera, Captain Majors summons Godzilla to battle the Chimera.
It doesn't take long for Godzilla to defeat the chimera and he manages to seal it away back in the containment it was in. The Sirens weren't too happy that Godzilla saved the crew and put Godzilla into a trance, causing him to fall asleep. One by one the Sirens manage to put the entire crew into a trance except Pete and Godzooky. Pete and Godzooky, while hiding, encounter the Minotaur and eventually outsmart it by trapping it in one of the labyrinths dungeon rooms. The Sirens who still aren't able to locate them decide that the best way to prevent the rest from escaping is by destroying their ship. However their powers are limited so they decided to merge into one being, with Morphea being the dominant one, and with their combined powers are then able to control the Chimera. Morphea then orders the Chimera to destroy the Calico. Godzooky distracts the Chimera temporarily while Pete tries to wake up Godzilla. Eventually the Chimera catches Godzooky in midair, just as Godzilla wakes up. Godzilla and the Chimera prepare to battle again but Morphea decides to help the Chimera by using her magic powers to merge their minds and bodies together. By doing this Morphea increases her height to a size greater than that of Godzilla's which also causes the Chimera to do the same. Now larger, the Chimera begins to overpower Godzilla. However, Godzilla eventually outsmarts the Chimera by causing it to charge off a cliff, and Godzilla was able to latch onto the cliff and pull himself back up. The Chimera falls into the ocean and is destroyed, with the Sirens presumably destroyed as well. This frees the Calico Crew from their trances and allows Godzilla to safely get them all off the island just as it disappears for another 1,000 years.