Belonging to the animal kingdom, Coelenterata, or more commonly known as the Phylum Coelenterata are the simplest group of animals that fall under the category of invertebrates . They are usually found living at the bottom of the sea, often attached to rocks. From genetics to ecology, Biology Topics cover a vast array of life sciences. Cnidaria – Definition, Classification, Reproduction Phylum Cnidaria or Coelenterata (Gr., koilos – hollow; enteron – gut) 1. Aquatic (living in water), mostly marine, a few such as Hydra are fresh water. Some of these species live in colonies (corals, Physalia), while others […] Detailed guide on Coelenterata , a group of aquatic organisms. Learn about their characteristics, classification and common FAQs. Phylum Coelenterata (Cnidaria) General Characteristic and Classification The Coelenterata may be defined as diploblastic metazoa with tissue grade of construction having nematocyst and a single gastrovascular cavity or the coelenteron.