''Astracantha'' is a genus of

planktonic Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...

phaeodaria Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They a ...

and the only member of the family Astracanthidae. They are an unusual family of marine

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s, but can be found across all oceans, from tropical to

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

and

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

waters.

Morphology

This genus is characterized by a skeleton or

theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...

comprised by 30 to 40 hollow spines radiating from the central focal point. Midway along each spine there are numerous short, irregularly spaced, outwardly curved branches that bear terminal thorns proximally (i.e. closer to the cell), but become terminally (i.e. further from the cell) smooth-pointed and slightly thicker. The length of their radial tubes is around 1.8 millimeters.

Distribution

The Astracanthidae are a very unusual family of

ns. ''

Astracantha paradoxa ''Astracantha'' is a genus of planktonic phaeodaria and the only member of the family Astracanthidae. They are an unusual family of marine protists, but can be found across all oceans, from tropical to Arctic and Antarctic waters. Morphology ...

'' was reported in 1908 by Valentin Haecker in five warm water stations in the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

and

Indian Indian or Indians may refer to: Associated with India * of or related to India ** Indian people ** Indian diaspora ** Languages of India ** Indian English, a dialect of the English language ** Indian cuisine Associated with indigenous peoples o ...

oceans. In 1986 it was reported for the first time from the

and

South Pacific The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

oceans. ''

Astracantha heteracantha ''Astracantha'' is a genus of planktonic phaeodaria and the only member of the family Astracanthidae. They are an unusual family of marine life, marine protists, but can be found across all oceans, from tropical to Arctic Ocean, Arctic and Antarc ...

'' was reported by Haecker twice, once in the Antarctic and once in the tropical Atlantic, and later has been found abundantly in the South Atlantic. In samples taken by the

oceanographic research ship Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology. It is an Earth science, which covers a wide range of top ...

''Eltanin'', both species were present but scarce at all localities, except the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...

, where ''A. paradoxa'' was absent. ''

Astracantha heteracanthoides ''Astracantha'' is a genus of planktonic phaeodaria and the only member of the family Astracanthidae. They are an unusual family of marine protists, but can be found across all oceans, from tropical to Arctic and Antarctic waters. Morphology ...

'' is found in deep waters of the

tropical Atlantic The Tropical Atlantic realm is one of twelve marine realms that cover the world's coastal seas and continental shelves.Spalding, Mark D., Helen E. Fox, Gerald R. Allen, Nick Davidson ''et al.'' "Marine Ecoregions of the World: A Bioregionalizati ...

Taxonomy

''Astracantha'' was first described by the zoologist Valentin Haecker in 1908. It is the only member of the family Astracanthidae, described by

Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; ; 16 February 1834 – 9 August 1919) was a German zoologist, natural history, naturalist, eugenics, eugenicist, Philosophy, philosopher, physician, professor, marine biology, marine biologist and artist ...

in 1887. Four species are known: * ''

'' * ''

Astracantha umbellifera ''Astracantha'' is a genus of planktonic phaeodaria and the only member of the family Astracanthidae. They are an unusual family of marine protists, but can be found across all oceans, from tropical to Arctic and Antarctic waters. Morphology ...

References

{{Taxonbar, from1=Q130356666, from2=Q25368816 Phaeodaria Rhizaria genera