part_of part of part of independent continuant secretory cell membrane-bounded organelle secretory granule PMID:29100657 https://orcid.org/0000-0003-2569-1939 | https://orcid.org/0000-0002-7535-4870 GO:0030141 Planarian_Anatomy A small subcellular vesicle, surrounded by a membrane, that is formed from the Golgi apparatus and contains a highly concentrated protein destined for secretion. Secretory granules move towards the periphery of the cell and upon stimulation, their membranes fuse with the cell membrane, and their protein load is exteriorized. Processing of the contained protein may take place in secretory granules.