Larger foraminifera: Reproduction and early stages of development in Heterostegina depressa

The process of reproduction (multiple fission) of the megalospheric gamont of Heterostegina depressa d'Orbigny, 1826 (Nummulitidae) is described. During this process, the protoplasm separates outside the parent test into the juveniles. The initial chambers receive some of the symbiotic algae from the parent protoplasm. The second chamber develops from the initial chamber by division, not by growth. The newly formed 2-chamber-stage receives a second set of symbiotic algae from the parent residual protoplasm. Thereafter, calcification takes place, and the first ectoplasm sheath is formed. The problem of alternation of generations is discussed. From the very small proportion of microspheric individuals found in Heterostegina species (fossil and recent) it is concluded that gamogony has been greatly reduced.