Only the spherical shell of Orbulina universa usually remains in sediments. In the living specimen shown, the sand-sized central sphere is surrounded by an abundance of delicate spines. Like most foraminifera, the shells and spines of this specimen are made up of calcium carbonate.
The numerous bright spots along the spines are smaller symbiotic organisms called dinoflagellates. These symbionts can number in the thousands per individual foraminifer. Even though foraminifers are single-celled heterotrophs, this particular species Orbulina universa is bound to live within the shallow photic zone because of its photosynthetic symbionts.
Photo used with permission from Dr. Howard Spero - photographer, UC Davis.