Tissue Level - Level of body organization
As you know a tissue is a group of cells similar in origin and structure that perform a specific function. The next level, is the tissue level of body organization which can be seen in coelenterates (Cnidaria and Ctenophora). These are made up of two germ layers ectoderm forming epidermis and endoderm forming the gastrodermis. The jelly fishes and their relatives are considered as the beginning of tissue organization and an excellent example of tissues, in Cnidarians is the nerve net in which the nerve cells and their processes form a definite tissue structure with the function of coordination.
Figure: Tissue Level