Lion's Mane Jellyfish - Capable of attaining a bell diameter of 8.2 ft, these jellyfish can vary greatly in size. At 120 feet in length, the largest known specimen was longer than a blue whale and is considered one of the longest known animals in the world.
"porpita porpita - the blue button jelly - is a neustonic species mostly found in the tropics; that is, it floats near the surface of the water. The circular disc is made of chitin and filled with gas, allowing these jellies to float. The tentacles (zooids) radiating from the disc do all the feeding."