Cnidaria
The phylum Cnidaria have many different forms, enormus medusae and corals, and box jellies with complex eyes. The name Cnidaria originates from the Greek word "cnidos," which translates to stinging needle. Cnidarians are diverse and come in various shapes and sizes but there are some basic attributes of their anatomy that most cnidarians share. The body wall of a cnidarian is made up of three layers, an outer layer called the epidermis, a middle layer referred to as the mesoglea, and an inner layer known as the gastrodermis. The epidermis houses a collection of different types of cells. These include epitheliomuscular cells which contact and enable movement, interstitial cells that give and create other cell types including egg and sperm, cnidocytes, and receptor and nerve cells which collect and transmit sensory information. They have no recognizable backbone or skeleton.