The acrosome reaction of the spermatozoa of the inarticulate brachiopod Lingula anatina

The spermatozoon of Lingula anatina has a head (about 1.5 m long), a midpiece (about 0.5 m long) and a tail with a tapered end. In the head, a fairly large pearshaped acrosome is present, in which an electron-dense structure (EDS) encloses the main part of the acrosome just inside the acrosomal outer membrane. The EDS has fine striations.