RadiolariaKingdom: ProtistaPhylum: SarcodinaClass: Actinopoda

Subclass: Radiolaria

What is Radiolaria?...See first these images for RADIOLARIA

Lamprocyclas maritalisLarcospira quadrangulaEuchitonia elegans

Lamprocyclas maritalis

Radiolarians are marine zooplankton belonging to the amoeboid protozoa. They produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. They are found as important fossils from the Cambrian onwards.

Radiolarians have many needle-like pseudopods supported by microtubules, called axopods, which aid in flotation. The nuclei and most other organelles are in the endoplasm, while the ectoplasm is filled with frothy vacuoles and lipid droplets, keeping them buoyant. Often it also contains symbiotic algae, especially zooxanthellae, that provide most of the cell's energy.

Morphological components of Radiolaria

Cross-sections through spumullarian radiolaria showing the relationship of the skeleton and the cell. From the UCL, London.

Many silicate radiolarians species (Spumellaria) from Haeckel (1904), artforms of Nature.

1- Subclass Radiolaria

a) Superorder Polycystinea

Include Spumellaria and Nassellaria. Their skeletons made

of amorphous silica (SiO2). They are present in sediments

since Cambrian

b) Superorder: Phaeodoria skeleton's silica is supported

by a matrix of organic matter (95% organic and 5% silica).

That means after death –polycystina only occurs. They

occur rarely in the sediments since Miocene.

2- Subclass: Acantharia skeleton of strontium sulfate crystals

(SrSO4), which do not fossilize.

Classification

Spumellaria images: a) Entactinosphaera, b) Albaillella, c) Actinomma and d) Dictyastrum, from Brasier 1980.

Nasellarian images: a) Campylacantha, b) Acanthocircus, c) Bathropyramis,

d) Podocyrtis and e) Cyrtocapsa, from Brasier 1980.

Radiolarians are single-celled, free-floating marine animals (protests) (marine

zooplankton) with spherical cells, mainly occur in the photic zone.

Size average between 100-2000 µm in diameter.

Living animal consists of protoplasm (endoplasm and ectoplasm) and nucleus

surrounded by layer/layers of lattice shell from which axopodia and spines

radiate. The ectoplasm contains numerous symbiotic algae, especially

zooxanthellae, that provide most of the cell's energy.

They reproduce asexually.

Shells sink after death to form the so-called radiolarian ooze of deep ocean

floors.

They occur near the seaward of the continental slope where divergent

surface currents bring up nutrients from the depths. They also blooms

seasonally with high numbers (100 000 /m3) at the polar regions with the

diatoms where silica and food are plentiful.

Living radiolarian, reproduction, distribution and ecology:

Radiolarians distribution in the modern ocean, from Brasier, 1980.

Radiolarians and sedimentation:

All radiolarians skeletons with strontium sulfate tests or organic materials are prone to dissolution after death.

Only polycystine radiolarians are the most resistant to dissolution.

Radiolarians oozes occur at the equatorial Pacific below zones of high productivity at 3000-4000 m depth. There one gram of sediments contains about 100 000 tests. They may also occur in marine diatomaceous oozes or in Globigerina and coccolith oozes.

Fossil radiolarians are frequently found in chert horizons. So, this chert is probably organic in origin.

Radiolarians general history

They occur in the sedimentary record since the middle Cambrian. Their record indicate that they did not flourish in the cooler periods as the diatoms.

Changes in species diversity of polycystine Radiolaria through time, from Brasier, 1980.

1. Radiolarian fossils in sediments used in determinations of the age of

the sediments that of particular importance for the oil industry when

the other fossils are absent.

2. Studies of the geological evolution of the continental land masses and

ocean basins.

3. Construction of the paleoecology and paleoclimatology of certain

periods and the Present.

Applications of Radiolaria