Coelenterata, also known as Cnidaria, is a phylum of aquatic animals that includes jellyfish, corals, sea anemones, and hydra. They are characterized by the presence of stinging cells called cnidocytes, which they use for capturing prey and defense. Let us understand the given statements and find out the incorrect one.

Tissue level of organization is present in Coelenterata
Coelenterata exhibits tissue level of organization, which means that the cells are organized into tissues that perform specialized functions. However, they lack specialized organs or organ systems.

Sea anemone exists in colonies
Sea anemones are usually solitary animals, but some species can form colonies. The colonies are formed by asexual reproduction, where the individual polyps divide and produce genetically identical offspring.

They have two layers of cells in their body i.e. they are diploblastic
Coelenterata is diploblastic, which means that their body is composed of two distinct layers of cells- the outer ectoderm and the inner endoderm. The mesoglea, a gelatinous substance, lies between the two cell layers.

They have a complete digestive system
Coelenterata does not have a complete digestive system, which means that they have only one opening for both ingestion of food and egestion of waste. The cavity that serves this purpose is called the gastrovascular cavity.

Incorrect statement: They have a complete digestive system
The given statement is incorrect because Coelenterata does not have a complete digestive system. They have a simple digestive system that lacks specialized organs such as a mouth, anus, or digestive glands. The gastrovascular cavity performs the function of digestion and distribution of nutrients throughout the body.