Xenophyophores are protozoans that live in the deepest parts of the ocean. Despite having been discovered around the turn of the 20th century, little is known about these single-celled organisms,largely because they are delicate and easily damaged when collected, easily mistaken for other organic and non-organic matter, and also because research in the deepest parts of the ocean remains difficult. Still, much interest surrounds these single-celled organisms partly because they are one of the largest single-celled organisms found in nature.
While their size varies and some have been found to be as small as 2 mm (0.06 in) wide, one species, the Syringammina fragillissima, has been reported to be as wide as 20 cm (8 in). Their overall shape varies as well. They can have frilly edges which resemble the Golgi apparatus within the eukaryotic cell or they may have a spherical sponge shape. Some are flat and others are four-sided tetrahedra.
Instead of blood, xenophyophores are filled with cytoplasm, intracellular fluid, and many nuclei which contain its genetic material. All of this is encapsulated within an organic, branched, tube-like structure called a granellare. Numerous in the deep ocean, xenophyophores move along the sea bottom like slugs. They excrete plasma to filter the sand out and only retain those nutritious particles and tiny animals, like nematodes, which are abundant deep sea floor.
Like amoeba, xenophyophores consume food by engulfing it using a structure called a pseudopodium. Most xenophyophores live right on the surface, although one species, Occultammina profunda is known to bury itself in sediment. Xenophyophores have at least one disgusting habit — they let their fecal matter, called stercomare, build up on themselves. The fecal matter mixes with their slimy secretions and produces long, string-like structures. This is, in part, where the organism gets its name, which originates from the Greek and roughly translates to "carrier of foreign matter."
Xenophyophores are abundant in some areas of the ocean floor, such as the abyssal trenches which are some 5,000 meters (16,400 feet) deep. Here, their density is great, dominating the life found in the area. While they have also been found just 1 meter (about 3 feet) deep they have also been found living some 7,000 meters (about 23,000 feet) deep within the ocean. Despite being relatively delicate in terms of collection for scientific purposes, they are rather strong in their ability to withstand the extreme pressures on the ocean floor, which may exceed 100 times the pressure at sea level. Xenophyophores probably don't have many predators, as few predators live so deep that they can harvest the abyssal plains.