arcualium

(plural arcualia))

an embryonic cartilaginous element from which the vertebrae form. There are primitively two pairs of endoskeletal elements in each metamere and on each side of the notochord, the interdorsals and basidorsals. In the gnathostomes (jawed fishes) there are two additional pairs ventrally to the notochord, the interventrals and basiventrals. All these elements are called arcualia and can fuse to a notochordal calcification, the centrum. Arcualia and centrum make a vertebra