Invented by merpeople and used as a guardian of the border of merpeople territory.
More information on the mermaid automaton contained in the excerpt from the journal entry of Professor Reginald H. Fettingis:
The submarine continued to descend and then leveled out and turned to the west. Suddenly the our lights glinted off a metallic being. In form it appeared similar to the merpeople, yet it gleamed with a goldish hue. Had the merpeople created their own automaton?
The mysterious creature raised a hand as if to motion us to stop. A curious instrument that looked like a combination of a trident and tuning fork was clasped in its other hand.
“Professor, have you seen such a creation before?” asked the captain.
“Never in all my explorations, sir,” I confessed as we continued to advance forward, ever approaching the inhuman figure.
“What is it holding? Surely it cannot puncture or harm the submarine with such a small weapon?” questioned Lieutenant Bradley.
As if in response, the automaton brandished the instrument. A flash, then a pulse was emitted. As the resulting wave struck the ship, it rocked and we covered our ears as a piercing shriek reverberated inside.
“Report! Any damage?” cried the captain as the shriek subsided.
“None… yet, Captain.” came the reply. “But more blasts like that could damage the hull.”
“The noise,” stammered an ensign. “It must have called more!” More metallic bodies began to swim into our lights.
“Reverse engines!” ordered the captain . . .