*3.1. Chemical*

Ech A (6-ethyl-2,3,5,7,8-pentahydroxynaphthalene-1,4-dion) was isolated from the sand dollar *Scaphechinus mirabilis* using an extraction method as previously described [25]. The purity of Ech A (>99%) was confirmed by liquid chromatography-mass spectrometry (Shimadzu LCMS-2020, Kyoto, Japan). We used 0.02% Ech A with saline solution.
