Definitions:

1. Describing the dorsal aspect or upper surface of certain animals. ADJECTIVE
   • The abdominal region of the sand dollar is smoother compared to that of the sea urchin.
2. It denotes the area of the body in echinoderms, such as starfish, sea urchin, sea cucumber, that is furthest to the mouth, typically located in the upper side. ADJECTIVE
   • The abdominal surface of the starfish is covered in tiny spines that aid in locomotion.
3. Of or relating to the surface or end opposite to the mouth in a radiate animal (starfish, sea urchin.) adjective
   • Researchers observed a significant change in the abdominal morphology of the sea urchin population.