Cystisoma is an amphipod, a creature with two kinds of legs, and they are almost entirely translucent. One major exception is their pale orange retinas, which each take up about half of its head.
Via Ocean Portal:
This hyperiid (in the genus Cystisoma) has only one pair of eyes—but they are very big. You can see them here as the entire surface of its head and the convex orange sheet of retinal cells in the bottom-right of the photo. Its eyes look almost exclusively upwards, possibly to watch out for animals overhead. This species is completely transparent. Even its gut (the bubble-like blue outline you can see in the picture) is see-through. This transparency keeps it from being seen by predators in the open ocean, where there is no place to hide. These hyperiids are much larger than most, reaching lengths of up to 7 inches. It helps to be see-through when you're that size.
The beauty in the video was "filmed in a special kreisel tank [a cylindrical tank for delicate creatures] on board the research ship RRS James Cook while working on the Mid Atlantic Ridge."