Globigerina, a genus of marine protozoans (one-celled organisms). The globigerina resembles the amoeba in structure, but has a spiny, multichambered shell composed of calcium carbonate. The shell contains pores through which pseudopodia protrude. The pseudopodia are extensions of cytoplasm the globigerina uses for locomotion and for collecting food. The main food of globigerinas is plankton.
Globigerinas live in vast numbers on or near the surface of the sea. When they die, the shells settle slowly to the bottom of the sea, forming deep beds of fine mud called globigerina ooze. This ooze gradually solidifies into chalk, a soft, powdery form of limestone. The chalk cliffs of England and France, and many limestone ridges of North America, were largely formed from globigerina ooze.
Globigerinas belong to the group Foraminifera (considered an order by some biologists, a phylum by others). The most common species is Globigerina bulloides. .)