[1] It is the only class within the subphylum Craniiformea, one of three major subphyla of brachiopods alongside linguliforms and rhynchonelliforms.

Craniata is divided into three orders: the extinct Craniopsida and Trimerellida, and the living Craniida, which provides most information on their biology.

The shells are inarticulate (lack a hinge with distinct tooth-and-socket connections) and are usually rounded in outline.

There is no pedicle; the rear edge of the body cavity is a smooth and flat wall perforated by the anus.

The lateral oblique muscles are widely spaced, extending forwards from the back of the ventral shell to the front of the soft body wall.