Flat Sea Star

The Royal Starfish is characterized by its bold colors. It has a purple granulated disk, which is the central region of the sea star, and the purple color continues to extend to its five arms. The margin of the sea star, which is its outline, is an orange color. Entomologist Thomas Say describes the sea star's margin as “articulated throughout”, meaning that the orange margin that surrounds the sea star is continuous, even at the joints of its rays. It also has white spines that are attached to the orange margin and tube feet at the ends of its rays.

The Royal Starfish feeds by swallowing its food whole and digesting it in its stomach, like other members of the genus Astropecten. However, unlike other species in the same genus, it consumes significantly more organisms. In a study investigating the stomach contents of 124 Royal Starfishes, scientists found that on average, each sea star has 12 organisms in its stomach, with the highest number of organisms recorded being 54. When comparing the number of organisms in the Royal Starfishes' stomachs to another study investigating the stomach contents of the Red Comb Starfish, it is revealed that the Royal Starfishes have much higher amounts. Also, one study investigating A. irregularis shows the same outcome, that there are more organisms in the stomachs of Royal Starfishes than A. irregularis, but in another study, the stomachs of both sea star species are relatively the same.