A leatherback turtle (Dermochelys coriaceaeating) eating thimble jellyfish (Linuche unguiculata)
This is a great video accompanying a nice paper on turtles and jellies [here]. Leatherbacks are obligate predators of jellies. Despite their size, leatherbacks are also difficult to study. Using planes to map out large swarms of jellyfish, scientists were able to predict the location of up to 22% of turtle sightings [paper]. In other words, find lots of jellies, find leatherbacks!
Thanks Arash for asking a great question and inspiring this post!