Gametogenesis and the antiquity of reproductive pattern in the Foraminiferida

Though the Foraminiferida have undergone immense diversification during the Phanerozoic as evidenced by shell form, reproductive pattern has evolved at a much more conservative tempo, The production of free-swimming, biflagellated gametes during the sexual phase of the life cycle is a widely shared feature of foraminiferal reproduction, occurring in all of the most diverse extant suborders, The fine details of this mode of gametogenesis. were compared in selected representatives (Cribrothalammina alba, Triloculina oblonga, Ammonia tepida) from three extant 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 separation of the pseudopodial and apertural cytoplasm (peduncle) from the rest of the foraminifer signaling the onset of gametogenesis, an enlargement and degeneration of the large gamontic nucleus reminiscent of ''Zerfall'', rapid proliferation of numerous gametic nuclei, the formation of large, prominent vacuoles throughout the cytoplasm, the emergence of paired flagella in association with each gametic nucleus and cytoplasmic differentiation of gametes, the production of spherical bodies 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 foraminifera.