Gromia sphaerica
Gromia sphaerica is a large spherical testate amoeba
Testate amoebae
Testate amoebae are single-celled protists partially enclosed in a simple test .They are commonly found in soils, leaf litter, peat bogs and near/in fresh water....

, a single-celled organism classed among the protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...

s and is the largest in the genus Gromia
Gromia is a widespread genus of marine and freshwater amoeboids, closely resembling some foraminiferans. It produces an organic test, which is ovoid or lobed and may exceed one millimetre in size; this resembles a small grape, in that its centre is fluid-filled but lacks organic matter, which is...

. It was discovered in 2000, along the Oman margin of the Arabian sea
Arabian Sea
The Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by the Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui in northeastern Somalia and Kanyakumari in India...

, at depths from 1163 to 1194 meters (3816 to 3917 feet). Specimens range in size from 4.7 to 38 millimeters (0.2 to 1.5 inches) in diameter. The test
Test (biology)
A test is a term used to refer to the shell of sea urchins, and also the shell of certain microorganisms, such as testate foraminifera and testate amoebae....

 (organic shell) is usually spherical in shape and honeycombed with pores. There are filaments on the bottom of the organism, where it is in contact with the seafloor, and it is mostly filled with stercomata (waste pellets).

In 2008, 30-millimeter (1.2-inch) specimens were found off the coast of Little San Salvador
Little San Salvador Island
Little San Salvador Island, Bahamas , is one of about 700 islands that make up the archipelago of the Bahamas. It is located roughly halfway between Eleuthera and Cat Island...

 in the Bahamas by researchers from the University of Texas. These Gromia were discovered to make mud trails as much as 50 centimeters (20 inches) in length. It was previously thought that single-celled organisms were incapable of making these kinds of trails, and their cause was previously a source of speculation. The mud trails made by the Bahamian Gromia appear to match prehistoric mud trails from the Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...

, including 1.8 billion year-old fossil trails in the Stirling formation
Stirling Range
The Stirling Range or Koikyennuruff is a range of mountains and hills in the Great Southern region of Western Australia, 337 km south-east of Perth. It is located at approximately and is over 60 km wide from west to east, stretching from the highway between Mount Barker and Cranbrook...

 in Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

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