Jellies Phantoms of the Deep Author:Aquarium of the Pacific Jellies: Phantoms of the Deep. They have no eyes. No brain. No heart. Sea jellies (also known as jellyfish)are made up of 95% water and yet they are alive and have inhabited earth's oceans relatively unchanged for more than 650 million years. find out more about these fascinating drifters in this special 11 minute video presentation.