After reading the title, you're probably picturing an adorable little mouse in scuba gear. Just to get the image out of your head and onto the screen, here's underwater Mickey:
The Illuminati are even underwater now.
Now that's that's over with:
The real sea mouse (Aphrodita aculeata) is not a mouse at all. It is instead a fuzzy, polychaete worm that lives on the ocean floor (up to 1000 meter depths). Sea mice are related to those funny little Christmas tree worms that inspired the plants in Avatar; a lot of polychaetes are spectacular to look at, either shining or glowing in the dark.
The sea mouse's body (up to 20cm in length) is covered with iridescent setae (i.e. hairs) that shine red or green depending on the angle of light. This is perfectly fair game for polychaete worms; many have spectacular gills, glow in the dark, or do other things that make humans jealous.
If you think the sea mouse looks like something strangely familiar or cleverly picked out that the sea mouse's generic name looks a lot like "Aphrodite," the Greek goddess of love, you get a cookie. Yes, that name is a reference to the worm's resemblance to human female genitalia when seen from below.
So, wait...this creature is a giant, sparkling pube? Why hasn't Japan turned it into a Pokemon yet?