13. 1. Jellyfishes are made up of more than 95% water. Their bodies are soft and lack a skeletal structure or outer shell. They are delicate and easily damanged. Jellyfishes require water to help support their body and if removed from their aquatic surroundings, they collapse and die. 2. Jellyfish are radially symmetrical. Jellyfish are symmetrical about a central axis that runs through the length of their body, from the top of their bell to the ends of their tentacles. They have a top and a bottom but they lack a left and right side and as a result differ from many other types of animals (such as mammals, reptiles, fish, birds, and arthropods) which exhibit bilateral symmetry. 3. A jellyfish has a simple digestives system with only one opening. A jellyfish takes food in through its mouth which is located on the underside if its bell. Food is digested in a sac-like structure called a coelenteron or gastrovascular cavity. Waste material is passed out through the mouth. 4. A common analogy used to describe the delicate way jellyfish pounce through the water likens the jellys' movements to 'a simple form of jet propulsion'. To move forward, jellyfishes take water into their muscular bell and then squirt it out behind them, creating a jet of water that propels the jelly forward. In addition to this form of movement, jellies also drift on water currents to move. 5. Jellyfishes have no brain, no blood, and no nervous system. Their senses are primitive and consist of a neural net, eye spots that can sense light from dark, and chemosensory pits that help them identify potential prey. 6. A jellyfishes' body consists of three layers. The outer layer is called the epidermis, the inner layer which lines the gastrovascular cavity is called the gastrodermis, and the middle layer consists of a thick substance called the mesoglea.