Oxygen-18 studies of recent planktonic Foraminifera: comparisons of phenotypes and of test parts.

Oxygen isotopic comparisons of phenotypes of Recent Planktonic Foraminifera with both normal and diminutive final chambers are compatible with a model in which the latter develop as a response to environmental stress. Isotopic evidence shows that Spheroidinella dehiscens is probably not a late-stage, aberrant form of Globogerinoides sacculifer.