Foraminiferida (informally foraminifera, foraminiferans, forams (pl.); foraminiferid, foraminifer, foraminiferan, foram (sing.); phylum Rhizopoda) Order (in some classifications, subclass Foraminifera) of testate, amoeboid protozoa in which the cell is protected by a test, consisting of one to many chambers, whose structure and composition is of great importance in foraminifera classification. The three main types are: (a) most primitively, a test wall composed of a secreted, chitinous-like, organic material called tectin, which also often forms an underlying layer in the other two types; (b) a test formed from agglutinated sedimentary particles, which may be cemented with an organic, calcareous, or ferric oxide cement; (c) a fully mineralized test, composed of secreted calcareous or siliceous minerals, of which the calcareous types (aragonite and calcite) are the most common. The arrangement of multiple chambers may be linear, spiral, conelike, etc. Numerous fossil foraminifera are known, usually less than 1 mm across; though some, like the fusilinids (Carboniferous to Permian) and nummulitids (Eocene to Oligocene) were appreciably larger (some measured up to 100 mm in diameter). All species live in marine environments. Agglutinated forms predominated in the Cambrian and Ordovician, presumably derived from a tectinous ancestor, while forms with fully mineralized tests appeared in the Ordovician and diversified greatly in the Devonian. The Foraminiferida are important zonal fossils, and some planktonic varieties can be used for stratigraphic correlation on virtually a world-wide scale. See GLOBIGERINA OOZE.

Foraminiferida (foram, foraminifer (pl. foraminifera, foraminiferan, foraminiferid; superclass Sarcodina, class Rhizopoda) An order (or in some classifications a subclass, Foraminifera) of amoeboid (see AMOEBA) protozoa in which the cell is protected by a test, consisting of one to many chambers, whose composition is of great importance in classification. The three main types are: (a) most primitively, a test wall composed of tectin (which also forms an underlying layer in the other two types); (b) a test formed from agglutinated sedimentary particles; and (c) a fully mineralized test composed of secreted calcareous or siliceous minerals of which aragonite and calcite are the most common. The arrangement of the chambers may be linear, spiral, cone-like, etc. Numerous fossil foraminifera are known, usually less than 1 mm across; though some, like the fusilinids (Carboniferous to Permian) and nummulitids (Eocene to Oligocene) were appreciably larger: some measured up to 100 mm in diameter. Most species live in marine environments. Agglutinated forms predominated in the Cambrian and Ordovician, presumably derived from a tectinous ancestor, while forms with fully mineralized tests appeared in the Ordovician and diversified greatly in the Devonian. The Foraminiferida are important zonal fossils, and some planktonic varieties can be used for stratigraphic correlation on virtually a world-wide scale. Accumulations of their tests make up a substantial part of certain geological formations (e.g. chalk deposits of the Cretaceous and Globigerina ooze).

foraminifera See FORAMINIFERIDA.

Foraminifera See FORAMINIFERIDA.

forams See FORAMINIFERIDA.