“Cnidaria” is Greek for “nettle” (“Introduction to Cnidaria”). The phylum Cnidaria includes freshwater hydras, jellyfish, and corals. Each of these invertebrates goes through transitions in body shapes. Jellyfish are the most unusual and complex of the phylum. Jellyfish belong to the class Scyphozoa, which means true jellyfish. Cnidarians are found in the Mediterranean and oceans. They can live in the ocean and coastal waters. But the main habitat of Cnidarians is the open ocean. Jellyfish can live in any ocean. There are deep-sea and shallow-water jellyfish. Some jellyfish, such as the Pelagia Noctiluca, can live wherever ocean currents decide to transport them ("). Phyla Cnidaria, Platyhelminthes and Nematoda"). A jellyfish's unique body structure helps it move, feed and protect itself. Their body is known as bell. During the bell phase, jellyfish, the jellyfish is mobile and is specialized for swimming. But in some Cnidarians, the bell stage occurs only in the embryonic stage ("Phyla Cnidaria, Platyhelminthes and Nematoda"). The jellyfish then produces an egg, which grows into a polyp (vessel stage) that is sessile (or immobile) living. Jellyfish have no back or front, left or right. They have no heart, head, legs or fins (Zimmer). They have a gastric pouch to hold food, the bell (body), oral arms that bring captured food to the mouth, tentacles that sting and kill prey, a mouth connected to digestive structures to digest food, and gonads that are reproductive organs. Jellyfish are also made up of 95% water (Northeaster University). Jellyfish move by expanding and contracting to push water behind them. Between each contraction and expansion there is a pause so that a vortex can be created... middle of the paper... Jellyfish do not have an excretory system, so the mouth hole also serves as the anus (“Pelagia Noctiluca”). A jellyfish does not have a circulatory system because it is radially symmetric, meaning they have a symmetrical arrangement of parts around a central point. (“Pelagia Noctiluca”)Jellyfish are a unique and interesting species. Even though jellyfish look complex, they are simple. They have very few internal systems, such as the respiratory, circulatory, excretory and nervous systems. Even though they do not have a nervous system they have the ability to sting and kill prey to survive. Chemicals can make them shine. They can move through expansions and contractions. They can reproduce both asexually and sexually. They are simple but still unique and interesting invertebrates. Jellyfish are fascinating and more complex than they seem.