There are clear transitionals in the fossils. Furthermore, I believe they are called foraminifera, but they have essentially the entire evolutionary history (in fossils).
You may be thinking of
Smooth Change in the Fossil Record although it does not cover forams. Forams are widely studied, parttly because they change so much in the fossil record and partly because they are incredibly useful in cross-correlating strata between differnt drill holes in exploring for oil.