An order of Granuloreticulosia in the class Rhizopodea. Foraminiferans are dominantly marine protozoa (single-celled animals), with a secreted or agglutinated shell, or test, enclosing the continually changing ameboid body that characterizes this and other orders of the superclass Sarcodina. Their unique combination of long geologic history, ubiquitous geographic distribution, and exceptional diversity of test composition, form, and structure make the foraminiferans the most useful of all marine fossils for stratigraphic correlation, geologic age dating of sediments, and paleoecologic interpretation. Although small in size, commonly less than 0.04 in. (1 mm), with a range between 20 micrometers and 4.8 in. (12 cm), foraminiferans may be abundant, more than 2600 living specimens having been recorded on 1.5 in.² (10 cm²) of sea floor. Their tests accumulated in great numbers and are recoverable from small quantities of sediment, rock outcroppings, well cores or cuttings, or ocean dredging and submarine coring.