My first steps to make this skin were to find some inspiration from the internet that would fit the theme of "Dark Depths". Glowing creatures and dark blues are the first thing that comes to mind, and I couldn't think of a much better variation. If I had more time, I think that I would have been able to come up with a more-creative idea. While searching, I discovered the skeletal jellyfish.

Here is one of the reference images I used for the jellyfish-like head and torso:

Image source

I know many people think of grotesque fish with sharp teeth when it comes to the bottom of the sea, but I wanted something more graceful.

In my skin, I worked very hard to create the long tentacles that skeletal jellyfish have, as well as the glow that emanates from them. The glow is meant to illuminate the dark mountain of rock behind it and the water above. At the feet, I put a burning color - almost like fire - to represent how the bottom of the ocean isn't really the bottom. Right below the homes of the animals living there, is the Earth's crust and eventually, its upper mantle (molten hot rock). As you can see, the jellyfish is pretty closed to the hot rock. This was partially because of the space I had on the skin and partially to represent an underground volcano or break in the crust. Either way, I'm happy with how the layout ended up.
I gave the skin eyes, symbolizing how everything in the ocean - up high or down low - is living in some way. The pixels on the outer layer of the eye are meant to represent some type of leg or tentacle - anything that would be slightly creepy at first sight.