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__CNIDARIAN 6th period__ By Seth Cruz and Taylor Weeks Purple Block

Cnidarians are free floating soft bodied animals that come in two forms, Medusa and Polyp. Cnidarians start out as polyp and then develop into Medusa. Cnidarians have a Gastrovascular cavity means that they have only one opening that serves as their mouth and anus. Cnidaria also have a three layer outer body, the epidermis, the mesoglea, and the gastrodermis. Cnidarians are very evolutionarily successful due to its nematocysts covered tentacles that allow cnidarians to hunt prey and move through the water efficiently.

__Body Structure__ Cnidarians are Acoelomate organisms meaning they have no body cavity or no fluid filled space in their bodies. There are two types of Acoelomate body structures. The first type composes of two layers known as the ectoderm and endoderm layers that are not separated by a cavity. The second type is similar with an additional layer called the mesoderm layer that is also not separated by a cavity. Cnidarians inherit the first type of acoelomate body s tructure. Cnidarians were the first organisms to be made of tissue. Most cnidarian organisms have two layers that compose the tissues, the epidermis(being the outer layer) and the gastrodermis.

Between the epidermis and gastrodermis is a translucent jelly like substance called the mesoglea. The mesoglea acts as structure support for cnidarian in the water just as humans have bone and cartilage as structural support on land. This is where the name “jellyfish” is derived from. Cnidarians have radial symmetry meaning a line of symmetry can be drawn any where on their surface. This is because cnidarians have a very circular structure. Notice how most cnidarian organisms have circular structure.

__Characteristics__ Examples of animals in the Cnidarian phylum are sea jellies. They are know as invertebrates, meaning they have no spine. They have many characteristics but the main characteristics of the Cnidarian animals are that they don’t have a spine, they live in both fresh and salt water, they have tissues and a simple nervous system, and have stinging cells called Nematocysts. Two of the common classes within cnidarians are invertebrates, and cnidocytes.

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