Antheridium fine structure and spermatozoid release in Laminaria digitata (Phaeophyceae)

Spermatozoids in Laminaria digitata exhibit fine-structural details typical for male brown algal gametes, except for the presence of well-developed chloroplasts and lack of an eye-spot. The most conspicuous features of mature antheridia are a specialized swelling of the cell wall (cap) and large amounts of mucilage surrounding the spermatozoid. Both components are involved in the explosive bursting of the antheridia, which is triggered by a hormonal factor.