PATTERNS OF SEXUAL REPRODUCTION IN DIATOMS

Sexual reproduction takes many forms within the diatoms. The variation has been classified by several authors, but in most cases the distinc tions between their main categories have depended on the number of gam etes produced per gametangium (and thus on how many zygotes per pair o f copulating cells), and upon whether fusion is oogamous, anisogamous or isogamous. These classifications are not themselves an adequate bas is for taxonomic comparison, which should be based on individual chara cteristics of the sexual process. Diatoms seem to be primitively oogam ous. In araphid pennate diatoms and some raphid diatoms the gametes an d gametangia are morphologically alike but physiologically distinct; o ne gametangium produces active gametes and the other passive ones. Thi s may be the primitive condition in pennate diatoms, providing a link to the oogamy of centrics via the morphological anisogamy of Rhabdonem a Kutz.