Flagellar Spines

Flagellar spines are a peculiarity of unknown function confined to male gametes of a few oogamous brown algae. The spermatozoids of Dictyota sp. are unique in possessing a longitudinal row of 12 very short spines on their single hairy flagella (these spermatozoids are basically biflagellate, but the second flagellum is reduced to its basal body only). Spines are absent on the distal 2.5– 3 µm of the flagellum, and on the proximal 10 µm. In some Fucales (Himanthalia, Xiphophora, and Hormosira), spermatozoids possess only a single spine, up to 1.0 µm long. In all these algae, each spine is made up of electron-dense material, located between the flagellar membrane and the peripheral axonemal doublets.