Foraminiferas have existed for many millions of years, one of the oldest fossilised examples comes from the Nummulitic Limestone found in Spain and dated to 45 million years old (nummulites are the name of a fossil species of foraminiferas).

Foraminifera Microscope Slide

Modern foraminifera are found both on the sea bottom and floating in the sea. Many of the specimens today are found by gathering sediments from the deep ocean.