Temporal range: 542–0 Ma[1]
Ammonia tepida.jpg
Live Ammonia tepida (Rotaliida)
Scientific classification

d'Orbigny, 1826




incertae sedis

Foraminifera (/fəˌræməˈnɪfərə/; Latin for "hole bearers"; informally called "forams") are members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell (called a "test") of diverse forms and materials. Tests of chitin (found in some simple genera, and Textularia in particular) are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment (i.e., are benthic), while a smaller variety float in the water column at various depths (i.e., are planktonic). Fewer are known from freshwater or brackish conditions, and some very few (nonaquatic) soil species have been identified through molecular analysis of small subunit ribosomal DNA.[2][3]

Foraminifera typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure.[4] These shells are commonly made of calcium carbonate (CaCO
) or agglutinated sediment particles. Over 50,000 species are recognized, both living (10,000)[5] and fossil (40,000).[6][7] They are usually less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm.[8]

In modern scientific English, the term foraminifera is both singular and plural (irrespective of the word's Latin derivation), and is used to describe one or more specimens or taxa: its usage as singular or plural must be determined from context. Foraminifera is frequently used informally to describe the group, and in these cases is generally lowercase.[9]


Alcide d'Orbigny, in his 1826 work, considered them to be a group of minute cephalopods and noted their odd morphology, interpreting the pseudopodia as tentacles and noting the highly reduced (in actuality, absent) head.[10] He named the group foraminifères, or "hole-bearers", as members of the group had holes in the divisions between compartments in their shells, in contrast to nautili or ammonites.[9]

The taxonomic position of the Foraminifera has varied since their recognition as protozoa (protists) by Schultze in 1854,[11] there referred to as an order, Foraminiferida. Loeblich and Tappan (1992) reranked Foraminifera as a class[12] as it is now commonly regarded.

The Foraminifera have typically been included in the Protozoa,[13][14][15] or in the similar Protoctista or Protist kingdom.[16][17] Compelling evidence, based primarily on molecular phylogenetics, exists for their belonging to a major group within the Protozoa known as the Rhizaria.[13] Prior to the recognition of evolutionary relationships among the members of the Rhizaria, the Foraminifera were generally grouped with other amoeboids as phylum Rhizopodea (or Sarcodina) in the class Granuloreticulosa.

The Rhizaria are problematic, as they are often called a "supergroup", rather than using an established taxonomic rank such as phylum. Cavalier-Smith defines the Rhizaria as an infra-kingdom within the kingdom Protozoa.[13]

Some taxonomies put the Foraminifera in a phylum of their own, putting them on par with the amoeboid Sarcodina in which they had been placed.

Although as yet unsupported by morphological correlates, molecular data strongly suggest the Foraminifera are closely related to the Cercozoa and Radiolaria, both of which also include amoeboids with complex shells; these three groups make up the Rhizaria.[14] However, the exact relationships of the forams to the other groups and to one another are still not entirely clear. Foraminifera are closely related to testate amoebae.[18]