Animals' internal body structures can either be coelomate, acoelomate, or pseudocoelomate. this means they may or may not have a heart a circulatory system lungs a body cavity

Animals' internal body structures can either be coelomate, acoelomate, or pseudocoelomate. This means that they may or may have not a "Body Cavity." Their body is hollow to the extent that they are flexible enough. They are positioned inside the body to protect the digestive tract and other organs.

Holozoic nutrition refers to the regular animal nutrition mode whereas saprophytic nutrition refers to the nutrition mode of fungi and bacteria.