GAMETOGENESIS AND THE ANTIQUITY OF REPRODUCTIVE PATTERN IN THE FORAMINIFERIDA

Though the Foraminiferida have undergone immense diversification durin g the Phanerozoic as evidenced by shell form, reproductive pattern has evolved at a much more conservative tempo, The production of free-swi mming, biflagellated gametes during the sexual phase of the life cycle is a widely shared feature of foraminiferal reproduction, occurring i n all of the most diverse extant suborders, The fine details of this m ode of gametogenesis. were compared in selected representatives (Cribr othalammina alba, Triloculina oblonga, Ammonia tepida) from three exta nt benthic suborders (Textulariina, Miliolina, Rotaliina respectively) to determine the extent to which this process had become modified in the Foraminiferida, Many of the detailed events and fine structure of gametogenesis are remarkably similar in these taxa, indicating little evolutionary change in the process, Similarities include: an initial s eparation of the pseudopodial and apertural cytoplasm (peduncle) from the rest of the foraminifer signaling the onset of gametogenesis, an e nlargement and degeneration of the large gamontic nucleus reminiscent of ''Zerfall'', rapid proliferation of numerous gametic nuclei, the fo rmation of large, prominent vacuoles throughout the cytoplasm, the eme rgence of paired flagella in association with each gametic nucleus and cytoplasmic differentiation of gametes, the production of spherical b odies or masses, and the release of numerous, small gametes which are isogamous and characterized by two unequal, acronematic flagella, The process is also broadly similar to that described for planktic foramin ifera.