"A jelly can grow or shrink according to the available food supply. If the cupboard is bare, jellies can 'de-grow,' shrinking in size so they need less food. They can re-grow again when food is more plentiful".
"Egg-yolk jellies sometimes carry passengers: crabs and amphipods have been found hitchhiking inside and on top of their bells. Young jack fish often can be found swimming among their tentacles."
Image From Monterey Bay Aquarium
"A group of jellyfish is often called a 'smack.' Many species of jellyfish are also capable of congregating into large swarms or 'blooms' consisting of hundreds or even thousands of individuals".
"The arctic Lion's mane jellyfish is the longest known animal; the biggest discovered had a bell (body), with a diameter of 2.3 m (7 feet 6 inches) and the tentacles reached 36.5 m (120 feet)".
Image from National Marine Sanctuaries