Pudgy Cusk Eel (Spectrunculus grandis)
As with eelpouts and wolf eels, cusk eels are ALSO not true eels. These deep-sea, ray-finned fish have a worldwide distribution, and tend to live close to the ocean floor (aka a bathydemersal lifestyle). They can grow over a meter long, making them some of the largest abyssal bony fishes.
The Pacific Ocean variety, like the ones we have observed at the Slope Base (2900 m) site, tends to have an elongated, laterally compressed, dark-colored body with a rounded, paler head and fins. They have long continuous dorsal and anal fins, similar to a rattail at first glance, but the cusk eel tails have a small caudal fin instead of tapering off to a point. They also have larger heads and sensory barbels that trail down beneath their chins. They can be distinguished from the snailfish that also hang out near the Slope Base infrastructure by their scales (snailfish are scaleless and have loose, gelatinous skin), barbels, pectoral fin shape, and differently shaped head.
Priede, et al. 2020: https://www.sciencedirect.com/science/article/pii/S0967064519301894