Comb jellyfish are jellyfish that live down in the midnight zone. The midnight is the third zone of the ocean. The trench is the last zone in the ocean. The first zone is the sunlight zone, the second is the twilight and the trench is the forth zone - this includes the Marianas trench)
Comb jellyfish have colored lights that change color and the lights go up and down and go by different color. Once one color is gone it pops up from the bottom. The comb jelly's head does not go out and in like an umbrella like other jellyfish do.
The comb jelly doesn't have long tentacles like most jelly fish. It's head is in the same place as other jellyfish - on top of the tentacles.
Note from the editor: I'm not really sure if he is talking about cone jellyfish or comb jellyfish as they are both true species. And I have no clue what the Marianas trench is or if he made it up. OK I googled Marianas Trench and it is really part of the ocean and of course Rehm had it right. Ah the things you learn from your six year old.