An antheridium or antherida (plural: antheridia) is a haploid structure or organ producing and containing male gametes (called antherozoids or sperm). It is present in the gametophyte phase of cryptogams like bryophytes and ferns, and also in the primitive vascular psilotophytes. Many algae and some fungi, for example ascomycetes and water moulds, also have antheridia during their reproductive stages.