ULTRASTRUCTURAL STUDIES ON SPHAEROPLEA ANNULINA (CHLOROPHYCEAE). II. SPERMATOGENESIS AND MALE GAMETE STRUCTURE1,2

The development and ultrastructure of the male gamete of Sphaeroplea annulina (Roth) Agardh have been investigated. Multiple mitoses each associated with phycoplast microtubules occur as a result of nitrogen deficiency in the culture medium. A regular cleavage of the cytoplasm delineated by microtubules then occurs, resulting in many young male gametes. During maturation the gametes are retained within a vacuolar envelope. Maturation entails reduction in nuclear size and chromatin condensation, loss of chloroplast thylakoids, endoplasmic reticulum and Golgi apparatus. The apical region where the two flagella are inserted consists of an apical cone and fibrous connections which lie distal to the basal bodies. The study supports the suggestion put forward in a previous paper: namely that the genus Sphaeroplea be retained in a separate order the Sphaeropleales.