FINE-STRUCTURE OF THE MALE AND FEMALE GAMETES OF ATRACTOMORPHA-PORCATA (SPHAEROPLEACEAE, CHLOROPHYTA) WITH EMPHASIS ON THE DEVELOPMENT AND ABSOLUTE-CONFIGURATION OF THE FLAGELLAR APPARATUS

Gametogenesis in Atractomorpha porcata Hoffman was initiated by the sy nchronous mitotic division of nuclei within a multinucleate gametangiu m. Uninucleate gametes were subsequently produced following two series of cytokinetic divisions. The first series involved the formation of phycoplast microtubules (phycoplastic cytokinesis), whereas the second series did not (nonphycoplastic cytokinesis). Centrioles were connect ed by a rudimentary striated distal fiber by the time they migrated to the planes of division preceding the first series of cytokinetic divi sion. These first divisions produced binucleate gametocytes. A well-de veloped flagellar apparatus lay near the cell surface in close proximi ty to each nucleus of the gametocyte prior to the second series of cyt okinetic divisions that produced the uninucleate gametes. As seen in a pical view, the paired basal bodies were directly opposed with no late ral displacement of their longitudinal axes. In lateral view, the pair ed basal bodies diverged from one another at an angle of 130-180 degre es (female) or 170-180 degrees (male) and were connected by an arched, distal striated fiber about 670-750 nm long and 600 nm at its widest part. Four electron-opaque, pyramid-shaped lateral bodies flanked the basal bodies in close contact with their undersurfaces. The flagellar roots demonstrated a cruciate arrangement, with s = 6-9 over 1 (female gametes) or 7-10 over I (male gametes) microtubules and d = 2 microtu bules. In male gametes, one of the multistranded roots was located clo se to the eyespot, and a second system of cytoskeletal microtubules wa s detected in ternally. Based on gamete ultrastructure, Atractomorpha porcata appears to be the most undifferentiated member of the genus.