Trimorphism in foraminifera (protozoa) - verification of an old hypothesis.

The formation of megalospheric schizonts by a microspheric agamont has been observed for the first time in a foraminifer, the living nummulitid Heterostegina depressa. This finding verifies part of the hypothesis of biologic trimorphism and forces retraction of the recent hypothesis, that the schizont is a separate apogamic species and not part of a trimorphic cycle. The production of large numbers of schizonts can explain high schizont densities in natural populations.