CNIDARIA
Otherwise known as Coelenterata, is a phylum that contains 10.000 species fo animal found in aquatic habittats. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many of their species have a hydro-static skeleton. In certain species, it is compared to a water filled ballon. Tubularia use columns of water-filled cells for support. Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, rather like sponges. Some species collect materials such as sand grains and shell fragments, which they attach to their outsides. Different types of colonial sea anemones often stiffen the mesoglea with sediment particles. Below is a cross section of what a standard species member of Cnidaria would look like: