Which of the following terms refers to the concept of organisms having a body cavity completely surrounded by tissue?

The term that refers to organisms having a body cavity completely surrounded by tissue is coelomate. In coelomate organisms, the coelom, or body cavity, is fully lined with mesoderm, which is a type of embryonic tissue. This lining allows for the development of complex organ systems and facilitates better movement and structure within the body.

For example, in coelomates such as humans and other vertebrates, this well-defined body cavity is crucial for the positioning and functioning of organs, as it provides a protective space and allows for the movement of tissues and organs as they perform their functions.

In contrast, acoelomate organisms lack a body cavity entirely, meaning their internal structures are solid and they have no space for internal organs to move freely. Pseudocoelomates possess a body cavity that is not entirely surrounded by mesodermal tissue, leading to a construction that does not support as complex an arrangement of organs as found in true coelomates. Invertebrates, on the other hand, refer to a broader category that includes many organisms, both coelomate and acoelomate, and is not specific to the presence of a body cavity surrounded by tissue.