adjacent to part of secretory granule acrosomal vacuole spider_anatomy 2014-12-29T17:21:58Z acrosome A structure in the head of a spermatozoon that contains acid hydrolases, and is concerned with the breakdown of the outer membrane of the ovum during fertilization. It lies just beneath the plasma membrane and is derived from the lysosome. SPD:0000732 GO:0001669 Peter Michalik acrosomal vesicle acrosomal complex anterior indentation of the sperm nucleus