ABSTRACT
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.
ABSTRACT
A single gamont of Heterostegina depressa released cells thought to be gametes. These sexual products were Feulgen stained and their nuclei were scanned with a microphotometer. Their mean absorption values (DNA contents) fell into 4 distinct classes: 0.71 AU (absorption units), 1.34 AU, 2.89 AU and 5.73 AU. The consistant increase by a factor of 2 indicated a definite nuclear status in each class. We propose that the respective DNA-contents belong to haploid isogametes, to zygotes immediately after fertilization, to zygotes after one replication, and to individuals after a second endocycle. The nuclei in agamonts rapidly became polyploid. This endoreplication is in contrast to cell cycles of other foraminifera, in which zygotic nuclei undergo metagamic divisions resulting in multinuclear agamonts. A 2 C-value of 0.19 pg DNA was obtained for H. depressa. The general morphology of the gametes resembles that of biflagellate gametes of other foraminifera. The gametes were 2.7 um long, contained a 1.5 µm-diameter nucleus, conspicuous lipid droplets and a vacuole of undetermined content. The two flagella were acronematic.