Solution

Phylum Coelenterata includes tentacle bearing, aquatic animals having a tissue level of body organization. Phylum Coelenterata is characterized by the presence of the following features:
(1) The presence of a single body cavity called coelenteron or gastrovascular cavity.
(2) Diploblastic animals, i.e., body wall composed of two layers of cells, an outer ectoderm, and an inner endoderm.
For examples, Hydra, Obelia, Aurelia, etc.
Thus option A is the correct answer.