Radiolaria Kingdom: Protista Phylum: Sarcodina Class: Actinopoda Subclass: Radiolaria What is Radiolaria?...See first these images for RADIOLARIA Euchitonia elegans Larcospira quadrangula Lamprocyclas maritalis

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. Lamprocyclas maritalis

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.

Classification 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.

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.

Living radiolarian, reproduction, distribution and ecology: 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.

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.

Applications of Radiolaria 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. Studies of the geological evolution of the continental land masses and ocean basins. Construction of the paleoecology and paleoclimatology of certain periods and the Present.