What class of joints is characterized as immovable?

The correct classification for joints that are characterized as immovable is synarthroses. Synarthroses joints are tightly connected by connective tissue or cartilage, allowing for no movement between the articulating bones. This immobility is crucial in areas of the body where stability is more important than flexibly, such as in the skull where the sutures securely join the cranial bones.

Understanding the other choices can help clarify why they do not fit the definition of immovable joints. Diarthroses refers to freely movable joints, such as the knee or elbow, which allow a wide range of motion. Amphiarthroses descriptions indicate joints that allow slight movement, presenting flexibility while still providing some stability, such as the joints between the vertebrae. Cartilaginous joints, which could include some amphiarthroses, are joints where bones are joined by cartilage but are not necessarily immovable as they may allow for limited movement. Thus, the distinct classification for joints that are completely immovable is synarthroses.