The Mermaid Scale is the Scale of the Mariner Tethys in Saint Seiya. It is a Scale that an ordinary Mariner would wear, the only one seen in the series.
In ancient days, Sailors would spend long amounts of time at sea. Over time, certain needs would come, and they would come hope telling of Mermaids, beautiful part woman, part fish that they had lain with. Of course, these were speculated to have been the Manatee, or Sea-Cow, due to a certain anatomical similarity between it’s female and the human female. Nevertheless, these legends continued to endure over the centuries, though no such creature has ever been confirmed.
The Mermaid Scales represent a Mermaid, a half-woman, half-fish being found in the folklore of several cultures, that would enchant sailors with their beautiful voices, and then kill them.