• (a.) Between the radii, or rays; -- in zoology, said of certain parts of radiate animals; as, the interradial plates of a starfish.
In`ter·ra'di·al adjective Between the radii, or rays; -- in zoölogy, said of certain parts of radiate animals; as, the interradial plates of a starfish. 
Type: Term Pronunciation: in′tĕr-rā′dē-ăl Definitions: 1. Situated between radii or rays.
situated between the radii or rays: interradial petals.