Concepts from regeneration research and from the extraxial-axial theory (EAT) are synthesized to determine the growth zones and extraxial-axial body wall homologies of asteroids. It is found that the growth zone at the asteroid arm tip produces the actinal, abactinal, and ambital surfaces of the arm tip and the primary skeletal components of the asteroid arm. The plates added in the growth zone cause the arms to grow outward. Asteroid ambulacrals, adambulacrals, and marginals are formed consistent with the ocular plate rule, and all are axial skeletal plates. The development of actinals, intermarginals, and dorsolaterals is developmentally secondary to the development of the axial skeleton. Midradial abactinal arm plates may form adjacent to the terminal plate, consistent with the ocular plate rule, or they may form secondary to superomarginals, such as when midradial abactinal plates are occluded from the tip of the arm by left/right coming together of distal superomarginals. Extraxial skeleton is present as centrally located abactinal disc plating. There is a boundary between the abactinal disc plating and the skeleton of the arms. The evolutionary-developmental event that led to the outgrowth of arms was acquisition of distal signaling in the full periphery that surrounds the arm tip (full-surround distal-signaling).