Buccalin, secreted in sea hare mollusc, is a modulatory neuropeptide acting presynaptically on nerve terminals to inhibit acetylcholine release.Mollusc: H-Gly-Met-Asp-Ser-Leu-Ala-Phe-Ser-Gly-Gly-Leu-NH2 or H-GMDSLAFSGGL-NH2