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

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

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

Arabian sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channe ...

, 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 The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...

, 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 island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the a ...

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 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 pꞒ, 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 th ...

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

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

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

bilateria The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...

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

Description

''G. 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 perhaps 8,000 years a ...

in size and in body appearance. When the sediment was removed from one of the specimens, it showed that the skin was similar to that of a

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 Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

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

External links

Endomyxa Amoeboids {{Cercozoa-stub