What does the space Jellyfish do?
When you hit a 'jellyfish' (called a Rifter in-game), you fly as normal but blinded for a split second. Though the Rifters do not directly damage your ship, the momentary blindness is dangerous due to the risk of running into oncoming debris or not having enough time to react to debris that appear when you regain your vision.
When you are at the beginning of a flight and your ship is still accelerating at a slow speed, you should still be able to predict if you will run into any debris after hitting a Rifter and adjust your path accordingly, as long as you stay wary of what is coming from the top of the screen.