Dictionary.net

Paired, segmented masses of mesodermal tissue that form along the length of the neural tube during the early stage of embryonic development. They give rise to the vertebral column and other tissues including voluntary muscle, bone, connective tissue, and the dermal layers of the skin.

Same as Protovertebra.

Any one of the individual embryonic segments out of which a particular segment of the body is subsequently developed.

A single segment in the body of an articulate animal.