Male gametogenesis ultrastructure of Codium fragile subsp. novae-zelandiae (Bryopsidophyceae, Chlorophyta)

Male gametogenesis was studied by light and electron microscopy in the dioecious siphonous green alga Codium fragile subsp. novae-zelandiae. Gametangia were formed on the sides of utricules. Initially, gametangia showed vegetative interphase nuclei and chloroplasts already with a mature structure with few thylakoid lamellae and a single starch granule. Then, mitotic divisions occurred, originating a proliferation of gametic nuclei. Features of the gametangial mitosis were similar to vegetative mitoses of other Bryopsidophyceae. The fusion of minute vesicles clearly delimited uninucleate portions of protoplasm with a large mitochondrion and chloroplasts. Ultimately, the gamete final shape was delimited, and the basal-flagellar apparatus developed. Mature gametes were liberated immersed in a mucilaginous material throughout an apical opening. They were elongated-ovoid in shape and showed two flagella, a hyaline anterior portion and a rear portion with two or three yellow-green chloroplasts. The nucleus was anterior, with abundant condensed chromatin and without nucleolus. A large 'inverted-V-shaped' mitochondrion was located in the anterior region of the gamete. Chloroplasts had poorly developed lamellae and a large starch granule. The basal-flagellar apparatus features were the typical for the class.