amphicoelous

Amphicoelous refers to a type of vertebral centrum, the main body of a vertebra, that is concave on both its anterior and posterior surfaces. This characteristic shape is found in the vertebrae of many fish, where it contributes to the flexibility of the vertebral column, allowing for efficient swimming motions. The opposing concave surfaces create a large space between adjacent vertebrae. This space is typically filled with a gelatinous or semi-fluid intervertebral disc. This arrangement, with the disc acting like a ball joint, permits a wide range of motion and allows the vertebrae to move against each other with minimal friction. In contrast, other vertebral types include procoelous (concave anteriorly, convex posteriorly), opisthocoelous (convex anteriorly, concave posteriorly), and amphiplatyan (flat on both surfaces). The amphicoelous condition is considered ancestral among vertebrates.