foraminiferan Amoeboid protozoan animal that lives among plankton in the sea. They have multi-chambered chalky shells (tests), which may be spiral, straight or clustered, and vary in size from microscopic to 5cm (2in) across. Many remain as fossils and are useful in geological dating. When they die, their shells sink to the ocean-floor to form large deposits, the source of chalk and limestone. Order Foraminiferida.

foraminiferan See FORAMINIFERIDA.