  Starfish typically show pentameral symmetry, and they are typically similar
in shape to a pentagram. Although starfish can evolve and live with other
numbers of arms, the dominant species always show pentameral symmetry. We used
mathematical and physical methods to analyze the superiority of starfish with
five arms in comparison with those with a different number of arms with respect
to detection, turning over, autotomy and adherence. In this study, we
determined that starfish with five arms, although slightly inferior to others
in one or two aspects, exhibit the best performance when the four
aforementioned factors are considered together. In addition, five-armed
starfish perform best on autotomy, which is crucially important for starfish
survival. This superiority contributes to the dominance of five-armed starfish
in evolution, which is consistent with the practical situation. Nevertheless,
we can see some flexibility in the number and conformation of arms. The
analyses performed in our research will be of great help in unraveling the
mysteries of dominant shapes and structures.
