Radiolarian

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Radiolarian

Radiolarians (also radiolaria) are amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
protozoa

Protozoa

Protozoan are microorganisms classified as unicellular eukaryotes. While there is no exact definition of the term "protozoan", most scientists use the word to refer to a unicellular heterotrophic protist, such as an amoeba or a ciliate....
that produce intricate mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
skeleton

Skeleton

In biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa....
s, typically with a central capsule dividing the cell

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
into inner and outer portions, called endoplasm and ectoplasm

Ectoplasm

Ectoplasm generally refers to the outer part of a cell's cytoplasm.Ectoplasm may also refer to:* Ectoplasm , a supposed physical substance that manifests as a result of spiritual energy or psychic phenomenon...
. They are found as zooplankton

Zooplankton

Zooplankton are the heterotrophic type of plankton. Plankton are organisms drifting in the Pelagic zone of oceans, seas, and bodies of fresh water....
throughout the ocean, and their skeletal remains cover large portions of the ocean bottom as radiolarian ooze

Radiolarian ooze

Radiolarian Ooze is a soft calciferous material that covers large areas of the ocean floor. It consists of the skeletal remains of radiolarians such as foraminifera and other minute organisms that have settled upon the ocean floor....
. Due to their rapid turn-over of species, they represent an important diagnostic fossil

Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
found from the Cambrian

Cambrian

The Cambrian is a geologic period that began about Mya at the end of the Proterozoic eon and ended about Ma with the beginning of the Ordovician period ....
onwards.

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Encyclopedia

Radiolarians (also radiolaria) are amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
protozoa

Protozoa

Mineral

Skeleton

Cell (biology)

Ectoplasm

Zooplankton

Radiolarian ooze

Fossil

Cambrian

The Cambrian is a geologic period that began about Mya at the end of the Proterozoic eon and ended about Ma with the beginning of the Ordovician period ....
onwards. Some common radiolarian fossils include Actinomma, Heliosphaera and Hexadoridium.

Description

Radiolarians have many needle-like pseudopod

Pseudopod

eruses4|eukaryotic cells|the Band|Pseudopod }}Pseudopods or pseudopodia are temporary projections of eukaryotes. Cells having this faculty are generally referred to as amoeboids....
ia supported by bundles of microtubule

Microtubule

Microtubules are one of the components of the cytoskeleton. They have a diameter of 25 Nanometre and length varying from 200 nanometers to 25 micrometers....
s, called axopods, which aid in the Radiolarian's buoyancy. The nuclei

Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
and most other organelle

Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s are in the endoplasm, while the ectoplasm is filled with frothy vacuole

Vacuole

A vacuole is a membrane organelle which is present in all eukaryotic cells. Vacuoles are essentially enclosed compartments which are filled with fluid such as water or various enzymes, though in certain cases they may contain solids which have been engulfed....
s and lipid

Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
droplets, keeping them buoyant. Often it also contains symbiotic

Symbiosis

The term symbiosis commonly describes close and often long-term interactions between different biological species. The term was first used in 1879 by the Germany mycology Heinrich Anton de Bary, who defined it as "the living together of unlike organisms"....
algae, especially zooxanthella

Zooxanthella

Zooxanthellae are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the Scleractinia corals and the tropical sea anemone, Aiptasia....
e, which provide most of the cell's energy. Some of this organization is found among the heliozoa

Heliozoa

Heliozoa, or sun animalcules, are roughly spherical amoeboids with many stiff, microtubule-supported projections called axopods radiating outward from the cell surface....
, but those lack central capsules and only produce simple scales and spines.

The main class

Class (biology)

A class is the taxonomic rank in the biological classification of organisms in biology below phylum and above Order .The orders of taxonomy are life, Domain , kingdom , phylum, class , order , family , genus, and species....
of radiolarians are the Polycystine

Polycystine

The polycystines are a group of radiolarian protists. They include the vast majority of the fossil radiolaria, as their skeletons are abundant in marine sediments, making them one of the most common groups of microfossils....
a, which produce siliceous skeletons. These include the majority of fossils. They also include the Acantharea

Acantharea

The Acantharea are a small group of radiolarian protozoa, distinguished mainly by their skeletons. These are composed of strontium sulfate crystals, which do not fossilize, and take the form of either ten diametric or twenty radial spines....
, which produce skeletons of strontium sulfate

Strontium sulfate

Strontium sulfate is the sulfuric acid salt of strontium. It is a white, odorless, crystalline powder, and occurs in nature as the mineral Celestine ....
. Despite some initial suggestions to the contrary, genetic studies place these two groups close together. They also include the peculiar genus Sticholonche
Sticholonche

Sticholonche is a peculiar genus of protozoan with a single species, S. zanclea, found in open oceans at depths of 99-510 metres. It is generally considered a heliozoan, placed in its own order, called the Taxopodida....
, which lacks an internal skeleton and so is usually considered a heliozoan.

Traditionally the radiolarians have also included the Phaeodarea

Phaeodarea

The Phaeodarea are a group of amoeboid protists. 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....
, which produce siliceous skeletons but differ from the polycystines in several other respects. However, on molecular trees they branch with the Cercozoa

Cercozoa

The Cercozoa are a group of protists, including most amoeboids and flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome or mouth as found in many other protozoa....
, a group including various flagellate

Flagellate

Flagellates are cell s with one or more whip-like organelles called flagellum. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla....
and amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s.
The other radiolarians appear near, but outside, the Cercozoa, so the similarity is due to convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action....
. The radiolarians and Cercozoa are included within a supergroup called the Rhizaria

Rhizaria

The Rhizaria are a species-rich supergroup of protists. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods....
.

Some radiolarians are known for their resemblance to regular polyhedra, such as with the icosohedron-shaped Circogonia icosahedra pictured to the left.

Fossil record

The earliest known radiolaria date to the very start of the Cambrian

Cambrian

The Cambrian is a geologic period that began about Mya at the end of the Proterozoic eon and ended about Ma with the beginning of the Ordovician period ....
period, appearing in the same beds as the first small shelly fauna

Small shelly fauna

The small shelly fauna or small shelly fossils, abbreviated to SSF, are biomineralization fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian period ....
- they may even be terminal precambrian in age. They differ little from later radiolaria.

Haeckel's radiolarians

German biologist Ernst Haeckel

Ernst Haeckel

'Ernst Heinrich Philipp August Haeckel' ,also written 'von Haeckel', was an eminent Germany biologist, natural history, philosopher, physician, professor and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in biology, including phylum, ph...
produced exquisite (and perhaps somewhat exaggerated) drawings of radiolaria, helping to popularize these protists among Victorian parlor

Citizen science

Citizen science is a term used for projects or ongoing program of Normal science in which individual volunteers or networks of volunteers, many of whom may have no specific scientific training, perform or manage research-related tasks such as observation, measurement or computation....
microscopists alongside foraminifera

Foraminifera

The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net....
and diatom

Diatom

Diatoms are a major group of eukaryote algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as Colony in the shape of filaments or ribbons , fans , zigzags , or stellate colonies ....
s.

Radiolarian

Description

Fossil record

Haeckel's radiolarians

Illustrations from Haeckel's Kunstformen der Natur (1904)

See Also

External links