Xenophyophores: Giant 1-celled Organisms of the Deep Sea

These are giant unicellular organisms found throughout the world’s oceans, at depths of up to 10,641 meters (6.6 miles). When first described in 1889, the xenophyophores were placed with the sponges. Later they were classified as testate amoeboids (Arcellinida), then in their own phylum of within the Protista. A recent genetic study suggests the xenophyophores are a specialized group of Foraminifera.

Xenophyophores are found in the greatest numbers on the abyssal plains of the deep ocean. They are placed in two orders in 13 genera with approximately 42 recognized species; one species, Syringammina fragilissima, is among the largest known single-celled organisms at up to 20 cm in diameter.

Abundant but poorly understood, xenophyophores are delicate organisms with a variable appearance; some may resemble flattened discs, angular four-sided shapes (tetrahedra), or frilly or spherical sponges. Local environmental conditions—such as current direction and speed—may play a part in influencing these forms. Xenophyophores are essentially lumps of viscous fluid called cytoplasm containing numerous nuclei distributed evenly throughout. Everything is contained in a ramose (highly branched) system of tubes called agranellare, itself composed of an organic cement-like substance.

Their glue-like secretions cause silt and strings of their own fecal matter, called stercomes, to build up into masses (called stercomares) on their exteriors. In this way, the organisms form structures that project from the sea floor; this characteristic is also the source of their name, which may be translated from the Greek to mean "bearer of foreign bodies". A protective, shell-like test is thereby agglutinated around the granellare, which is composed of scavenged minerals and the microscopic skeletal remains of other organisms, such as sponges, radiolarians, and other foraminiferans.

(read more: Wikipedia)