GAMETOGENESIS AND THE LIFE-CYCLE OF THE FORAMINIFER AMMONIA-BECCARII (LINNE) FORMA TEPIDA (CUSHMAN)

Ammonia beccarii forma tepida, a common nearshore foraminifer that is well-known for its repeated asexual generations in culture, showed a very high incidence of gametogenesis in fresh field collections from Sapelo and Cabretta Islands, Georgia, taken from spring to early fall during 1990 and 1991. Yellow to yellowish-brown, non-reproductive gamonts build ''reproductive cysts'' of sediment and detritus, and loose their cytoplasmic coloration during the early stages of gametogenesis. Just prior to gamete release, the cytoplast expands to rill the terminal chamber and begins to swarm with active gametes. Gamonts shed the reproductive cyst and release numerous, small (approximately 2 mum), biflagellated gametes directly into the surrounding seawater via the aperture. After gamete release is nearly finished, predatory protists (dinoflagellates, ciliates) enter the test and feed on undifferentiated cytoplasm and unreleased gametes. Most gamonts range in size from about 130-420 mum, exhibit dextral coiling (88%), and have a proloculus that measures from about 27-48 mum. The life cycle of Ammonia beccarii forma tepida includes both sexual and asexual phases and is probably best characterized as a facultative alternation of generations.