I never knew...
http://en.wikipedia.org/wiki/XenophyophoreXenophyophores 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 a granellare, 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.