Because eels aren’t scary enough, lets combine it with a shark.
Glad evolution worked that one out.

It was an eel-shaped shark with almost no scales at a time when sharks came in more shapes than they do today and had even more variety in their feeding adaptations.
About eight inches (20 cm) long, it swam with some help from its fins, but also relied on whole-body locomotion to move.
The fish also had teeth sufficient for eating shellfish.

Late Mississippian
Bear Gulch Limestone
Fergus County, Montana, USA
35mm ventral view of a female shark on 60mm x 80mm slab
Shark, Bear Gulch Limestone