"Ophiactis brachyaspis", a type of brittle star, has a star-shaped body, and the number of arms varies from 4 to 7.The general way of walking a brittle star with five arms has been studied so far, and the usage of the arm when an individual who has lost the arm moves has also been observed.However, there were no reports of how to walk an individual with an arm number other than 5 while being intact.The research group worked to unravel the questions, "Why is it okay to have different numbers of limbs?" And "How do animals with no front, back, left, or right determine the" front "?"

　The research group touched the tip of the brittle star's arm to induce escape behavior, and investigated how individuals with different numbers of arms move using their arms.As a result, brittle stars tend to escape counterclockwise or clockwise from the touched arm in the direction of the "two next" arm, and at the same time move and row the arms on both sides of the leading arm at the same time. It was clarified using a mathematical model that there was a tendency.

　In this study, it is important how many arms are next to each other when tracing counterclockwise or clockwise from the stimulated arm, and no matter how many arms are in total, the movement of the individual is large. It turned out that the mechanism does not cause any problems.If this result can be applied to, for example, a "brittle star type mobile robot", it is thought that it will demonstrate excellent performance in places where undulations are severe and skillful turning according to the environment is required, and it will be active in disaster sites and space environments. Is expected.

Paper information:[Journal of the Royal Society Interface] A general model of locomotion of brittle stars with a variable number of arms