Jellies are a type of Noise. Noise #29-#32 are in this family.
Noise #29 - Jelly Madchester
Noise #30 - Jelly Swechno
Noise #31 - Jelly Neocoustic
Noise #32 - Jelly Germanic
During battle, Jellies attack by sending lightning bolts to each other. If Neku gets hit, damage is dealt to him. Those who received lightning bolts soon after clone themselves, which may result in a Jelly Madchester/Swechno for a Madchester or a Jelly Neocoustic/Germanic for a Jelly Neocoustic. Jelly Neocoustics/Germanics also can attack by grabbing Neku by their big tentacle, then draining HP. Jellies can extend their arms, then drift around, causing damage and possibly immobilization. The Jelly Swechnos and Jelly Germanics cannot multiply. Jellies are often contained in the shark-mouth noise symbols during Joshua's week. The second split forms have the same amount of health as their counterparts (610 and 980) and the same weakness/resistance. The "mutants" give more EXP for their defeat, and hold different pins. You should attack the jelly madchester/neocoustic first because if you defeat them, no more jellies con be spawned. But you might want them to spawn jellies to get some more EXP. This might be risky since the more jellies you have, the bigger chance you might get hit by their lightning pass attack since they "pass" deadly bolts of lightning through every jelly.
Jelly Noise