''Gromia sphaerica'' is a large spherical testate amoeba, a single-celled

eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

organism and the largest of its genus, '' Gromia''. The genus itself contains about 13 known species, 3 of which were discovered as late as 2005. It was discovered in 2000, along the Oman margin of the

Arabian Sea The Arabian Sea () is a region of sea in the northern Indian Ocean, bounded on the west by the Arabian Peninsula, Gulf of Aden and Guardafui Channel, on the northwest by Gulf of Oman and Iran, on the north by Pakistan, on the east by India, and ...

, at depths around . Specimens range in size from in diameter. The

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film) ...

(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, specimens were found off the coast of Little San Salvador in the

Bahamas The Bahamas, officially the Commonwealth of The Bahamas, is an archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of its population. ...

by researchers from the University of Texas. These ''Gromia'' were discovered to make mud trails as much as in length. It was previously thought that

single-celled A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell (biology), cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic ...

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 ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

, including 1.8 billion year-old fossil trails in the Stirling formation in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. Because the tracks of ''Gromia'' resemble the 1.8 billion year old traces that were believed to represent the traces of complex

bilateria Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left� ...

n worms, said tracks could have been a result of similarly giant single-celled organisms instead of complex animals.

Description

''Gromia sphaerica'' mainly resembled a

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...

in size and body appearance. When the sediment was removed from one of the specimens, it showed that the skin was similar to that of a grape's skin, but much softer when touched.

Tracks

The tracks that ''G. sphaerica'' makes on the muddy sea floor are similar to the tracks of animals from the

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

period. In some of the photos, the tracks can be seen as being curved. File:Gromia-field wInset.jpg, Multiple individuals of ''Gromia sphaerica'' on the slope of Exuma Valley, together with a shrimp for scale. The shrimp is about 10 cm long and maintains a horizontal position. Inset: details of individual traces.

References

Endomyxa Amoeboids Rhizaria species Protists described in 2000 {{Cercozoa-stub