Acoelomate

A solid-bodied animal that doesn’t have a body cavity, which is the space between the digestive system and the body wall is called acoelomate. Simple animals don’t have a body cavity like higher animals do. In mammals, the gut (which is a hollow in and of itself), heart, and lungs are all inside the coelom. Animals that are acoelomate are bipedal and triploblastic, which means they have three layers: the ectoderm, the endoderm, and the mesoderm. They can move forward and have some cephalization, which means that some of their nerves and sense organs are centralized in the head.