A characteristic of the phylum coelenterata is that

A characteristic of the phylum Coelenterata is that they possess a gut with a single opening. Coelenterates, also known as cnidarians, are a group of aquatic animals that includes jellyfish, coral, and sea anemones. Their gut has a single opening, which functions as both a mouth and an anus. This means that food enters and waste leaves through the same opening. This type of digestive system is called a gastrovascular cavity, and it is a defining characteristic of the phylum Coelenterata. The other options are not characteristics of Coelenterates - most of them are marine is true but not specific to Coelenterates, they do not possess numerous pores on their body, and they are not bilaterally symmetrical.