Jellies consume prey with long “oral arms”, which are frilly projections extending form the mouth.
These arms are covered with stinging cells and wrap around and engulf food. This is a close up of one of these arms, gliding over a piece of glass. This arm is about 10 cm long.
Below is an extra close up. We’re looking at about 1cm of area. The opaque dots and bumps are bundles of stingers, each one on its own cell. You can actually see individual cells contracting.The long tube-like structure visible in the middle of the arm is where the two halves fold together, and where food is transported to the stomach.
These videos are of a species called Pelagia noctiluca, and were taken by me with animals I have raised in the lab.
The Helm Lab Blog 
Whoooaaaaa those are cool. Do the stingers inject or secrete anything or are they just sharp or something? What do jellies eat, and how long does it take them to consume and digest their food?
The stingers inject a toxin that is very painful, and can leave a dark bruise for several weeks. This species eats primarily fish and other jellyfish, as well as small crustaceans. It only takes about a minute to wrap their arms around big prey, and a few seconds for something small like a little shrimp (seen in the first video). It takes a few hours to a day to fully digest food, though it also depends on temperature. Good questions!
It’s amazing how quickly they wrap their arms around the food.
Do jellyfishes eat fish? What do they eat and how do they eat
Some jellies, including this species, do eat fish. They catch food with their tentacles, then wrap their oral arms around the food (you can see here their oral arm wrapping around a very small shrimp). The food is then transported along the oral arms to the stomach (which is in the bell) where the food is digested. When they are done digesting, the waste is expelled out of the mouth.
That was one of my 7th graders asking questions up there. 🙂 I think he will be a scientist later in his life.
Another question on this topic from another 7th grade student. How do jellyfish sting and can it kill someone?
Jellyfish sting with specialized cells on their tentacles, or bodies. Most jellies stings can’t be felt by people, but a few jellyfish can kill people!
Here is another 7th grade question.
What is in jellyfish that make the sting hurt? I think we are very curious about jellyfish stings. . . maybe because we are headed to SeaCamp this spring!
Jellyfish have specialized toxins that they inject into skin when they sting people. Most jellies can’t sting people and/or their toxin don’t work on people. However, the toxins of a few jellies can sting people, using toxins they inject.