Chris Hutchinson, age 9, of Florence, S.C., for his question:

WHAT IS AN AMPHIOXUS?

An amphioxus, also called a lancelet, is a small sea animal that lives in shallow water. Many consider him to be the link between the vertebrates and the invertebrates. He has no distinct brain, but he has a nerve cord running along his back that is somewhat like the spinal cord of animals with backbones.

The amphioxus has an organ called the notochord instead of the hard, jointed backbone of the vertebrates. It is a rather stiff rod of cartilage, found along the back just under the nerve cord.

The primitive form of the backbone makes the slender amphioxus more like a vertebrate than an invertebrate.