During an expedition, a scuba diver saw an animal use stinging tentacles to capture and eat its prey. Which animal did the diver see?

The animal involved in this scenario would most likely be some form of larger jellyfish of the phylum Cnidaria. The scuba diver should be very careful in this sort of situation, as larger jellyfish such as this in certain parts of the world sometimes sting with venom that can prove fatal to human beings, not just marine life.