Valve morphogenesis in selected centric diatoms

Abstract

The traditional taxonomic affiliation of the diatom Ardissonea crystallina (C. Agardh) Grunow has been recently questioned, as it exhibits a mixture of polar centric and araphid pennate characters. Overall valve architecture and mode of sexual reproduction suggest that araphid pennates are its closest relatives. On the other hand, recovered molecular phylogenies consistently place it among the polar centrics. Our investigation of the earliest stages of valve morphogenesis, formation of the basal silica layer, adds to the argument that A. crystallina is indeed a polar centric diatom. We compared developmental stages in A. crystallina with unequivocally centric diatoms (non-polar Hyalodiscus stelliger and polar Biddulphia tridens) and published literature for araphid pennates and determined that A. crystallina has evolved an apparently unique mode of valve development. The significance of valve morphogenesis in better understanding diatom evolution and diversification is discussed.