EVERYDAY SCIENCE

Detailed explanation-1: -Answer and Explanation: Cnidarians have a very simple body plan with only one body opening. This opening is considered to be both the mouth and the anus. It leads to a space called the gastrovascular cavity, which serves to digest food as well as expel waste.

Detailed explanation-2: -Cnidarians have an incomplete digestive system with only one opening; the gastrovascular cavity serves as both a mouth and an anus.

Detailed explanation-3: -Most cnidarians are marine and all are carnivorous. They have tissues but no organs and their digestive cavity has one opening which serves as both their mouth and anus.

Detailed explanation-4: -Cnidarians are radially symmetrical (i.e., similar parts are arranged symmetrically around a central axis). They lack cephalization (concentration of sensory organs in a head), their bodies have two cell layers rather than the three of so-called higher animals, and the saclike coelenteron has one opening (the mouth).

Detailed explanation-5: -There are two basic cnidarian body shapes: a polyp form, which is attached to a surface; and an upside-down free-floating form called a medusa.