Foraminifera (Lat. foramen, an opening, and ferre, to carry), an order of the protozoa, of the class of rhizopods, having the power of projecting and retracting through openings in their calcareous shell temporary thread-like prolongations (pseudopodia) of sarcode, or the gelatinous protoplasmic substance of which the body is composed; by these processes they move and obtain food; they differ from amoeba in having a shell, and very long slender pseudopodia, interlacing with each other; they have no nucleus nor contractile vesicle, like the amoeba. The shell is often very complex and beautiful, enclosing the sarcode body, which has no structure nor definite organs, and yet has the power of making a calcareous or sandy shell. The shell may be single or many-chambered, the latter produced by the budding of the former. Placed very near the bottom of the animal scale, structureless and without permanent organs, they yet perform all the great physioiogi-cal functions of life, digestion, growth, reproduction, secretion, and locomotion. They are mostly microscopic, though the nummulite attained the diameter of an inch.

They are all marine, and are distributed all over the world; they have been dredged from a depth of nearly three miles in the vicinity of Spitzbergen. They were among the earliest created animals, and the oldest known fossil, eozoon, is a foraminifer; the great chalk deposit of Europe, wide as the continent, and sometimes nearly 1,000 ft. deep, is almost entirely made up of the foraminiferous globigerina, not to be distinguished from forms now living in the deepest Atlantic basin; the building stone of Paris is largely composed of foraminifera.