Jelly Fish

2 Pages 585 Words

Jellyfish
Few marine creatures are as mysterious and intimidating as the Jellyfish. Though jellyfish are easily recognized, the jellyfish is often misunderstood. Jellyfish belong to the phylum Cnidarians. Sea anemones, sea whips, and corals are also a part of the group. Cnidarians has three major classes, which are Hydrozoa, Scyphozoan, and Athoza. Hydrozoa are primitive fern-like creatures. The Hydrozoa group also produces small jellyfish. The Scyphozoans are adult jellyfish, or medusa. The Scyphozoans are the most common jellyfish. The last group is the Anthozoa which are the sea anemones. Jellyfish are believed to have arisen in the late Precambrian period. During the Precambrian period earth formed, the first tectonic plates arose and began to move, eukaryotic cells evolved, the atmosphere became rich in oxygen, and the first animals evolved. Even though the life of the late Precambrian period is poorly represented by fossils, a few invertebrates including creatures resembling jellyfish and worms have been discovered.
A jellyfish is an invertebrate made up of ninety five to ninety seven percent water, three percent protein, and one percent minerals. The shape and size of the jellyfish varies, but most are bell or umbrella shapes. Most jellyfish are semi-transparent or glassy, and their sizes range from one inch to a foot across in size. Jellyfish inhabit every major oceanic and freshwater area of the world. They are capable of withstanding a wide range of temperatures and salinities. Most live in coastal waters, but a few are able to withstand depths of about 12,000 feet or more.
A jellyfish has no brain, head, spine, eyes, or heart. Instead of a brain, a jellyfish possess a nervous system, also known as a nerve net. The nerve net consists of receptors capable of detecting light, odor, and other stimuli and coordinating responses. Jellies do not posses eyes but some jellyfish have ocelli. Ocelli are light...