Biflagellate spermatozoids in the Dictyotales: the structure of gametes and gametangia in Zonaria angustata (Dictyotales, Phaeophyta)

The spermatozoids of Zonaria angustata (Kutzing) Papenfuss (Phaeophyta) are biflagellate, and not uniflagellate as reported in other species of the Dictyotales. The anterior flagellum is 20–27 μm long and, in addition to mastigonemes and a terminal acronema, has a row of 23–33 spines distributed along its length. The posterior flagellum is very short, 1–1.5 μm long. Gametangial walls are not contiguous and sterile cortical cells occur between oogonia. The outer tier of the antheridia consists of sterile cells containing numerous physodes. It is argued that these characteristics of Z. angustata indicate that the order Dictyotales is more closely related to other brown algae than was previously thought, and the possibility of a phylogenetic relationship between the orders Dictyotales and Cutleriales is discussed.