Phylum Cnidaria
Cnidarians are soft bodied and are radially symmetric. They are carnivorous and have tentacles around their mouth. They are the simplest animals to have body symmetry and specialized tissues. Cnidaria get their name from Cnidocytes, which are stinging cells located on their tentacles. They use these Cnidocytes to defend themselves and capture their prey. They have a structure called a nematocyst, which is poison- filled and contains a tightly coiled dart, which they use to sting their prey or enemies. There are two types of Cnidaria: Polyps and Medusas. Polyps have cylindrical bodies with an upward pointing mouth and/or arm-like tentacles. They are sessile, which means non-moving. Medusas are mobile and have a bell shaped body with a downward facing mouth. Each Cnidarian has a body wall that surrounds the internal spaces called a gastrovascular cavity, the digestive chamber. Cnidarians are made up of the epidermis which is the outer layer, the mesoglea that is the inner layer, and last, the gastroderm; the digestive area. Digestion is extracellular, which means it happens outside of the cell. It finishes intracellularly in the gastroderm. Any materials not digested are passed out through the mouth. After digestion, nutrients get transported by diffusion through the body. Metabolic waste is released through the body walls. Cnidarians move by using circular and longitudinal muscles simultaneously that also work with gastrovascular water. This is called a hydrostatic skeleton. Cnidarians can produce sexually, as well as asexually. There are three groups of Cnidaria: Schyphozoa are jellyfish, Hydrozoa, which are hydras and relatives, and Anthozoa, that are sea anemones and corals.