Observations on Iridia diaphana, a Marine Foraminifer

SYNOPSIS. Iridia diaphana , a marine foraminifer, was used as a subject for observations on grano-reticulate pseudopods. The organism readily forms a pseudopod net and its behavior is roughly predictable. Test composition varies with the environment; test shape is more constant. Pseudopod form and structure were observed by transmitted plane and polarized light microscopy, by freeze-drying and scanning electron microscopy, and by thin section studies in the transmission electron microscope. Rigidity is probably due to the numerous 250 A dia. microtubules in the pseudopods. Other organelles observed include mitochondria, vesicles and vacuoles. The plasmalemma may have numerous villous projections. Pseudopod form in I. diaphana does not closely resemble that of Allogromia laticollaris as reported by Wohlfarth-Bottermann (25). A pseudopod may be composed of several membrane-bound units of cytoplasm, or of a single unit of cytoplasm. A reassessment of the theories of the mechanism of cytoplasmic streaming in foraminiferan pseudopods is necessary.