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SYNOPTIC DESCRIPTION OF PHYLUM RADIOLARIA

SYNOPTIC DESCRIPTION OF PHYLUM RADIOLARIA

EUKARYA> CHROMALVEOLATA> RHIZARIAE> RADIOLARIA
RADIOLARIA LINKS

Introduction

Hierarchical Classification

Descriptions of the phylum come from Kudo (1966), Grell (1976), Cachon et al. (1990), Febvre (1990), Febvre-Chevalier (1990), Patterson (1999); Cachon and Cachon (1978), and Smith and Patterson (1986).

I. SYNONYMS: Sarcodina, radiolaria.

II. NUMBER: > 4,000 species.

III. PHYLUM CHARACTERISTICS

  • A. Structure
    • Cell Form: Unicells with radiating axopods (text with tooltip) An axopod is a thin pseudopodium that is permanent and stiff due to the presence of an internal microtubular structure. This is characteristic of the Actinopodotista. , feeding structures supported by bundles of microtubules, usually mineralized.
    • Flagella: Motile swarmers (text with tooltip) Crystal swarmers are biflagellate motile propagules that are produced by certain 'radiolarians'. They sparkle due to internal crystalline inclusions. They may be gametes. with 2 flagella, which seem to be inserted laterally with one directed anteriorly (text with tooltip) An anteriorly-directed flagellum extends in the direction of the motion of the motile cell. The interpretation is that the flagellum functions by pulling the cell. and the other directed posteriorly (text with tooltip) Recurrent flagella bend to the posterior end of the cell. Typically, they are identified as recurrent when anteriorly-directed flagella are present. .
    • Basal Bodies: Probably perpendicular (text with tooltip) Basal bodies are perpendicular (or orthogonal) when their orientation relative to each other is at a right angle. .
    • Cell Covering: Naked but with an internal skeleton ( test (text with tooltip) A test is an external covering that is secreted or constructed by secretions from the cell. I distinguish it from a cell wall in that a test is not appressed to the plasmalemma. In fact, sometimes the cell can leave the test entirely. ) of strontium sulfate, silica, or organic material.
    • Chloroplasts: Some with endosymbiotic (text with tooltip) An endosymbiont is a living cell that has become symbiotic within the host cell. Thus, the endosymbiont and the host become interdependent. Mitochondria and chloroplasts (among others) are common endosymbionts. dinoflagellates or haptophytes.
    • Food Reserves: Oil.
    • Mitochondria: Present with tubular cristae (text with tooltip) Mitochondrial cristae that form as extended saccate structures or tubes are called tubular cristae. .
    • Golgi (text with tooltip) Golgi apparatus (also called dictyosome) is an internal membrane system of stacked flattened sacs. They occur in nearly all eukaryotes and are involved in storing and secreting cellular products. : Present.
    • Nucleus: Contained within a capsule which is often mineralized.
    • Centrioles: Probably occur.
    • Inclusions and Ejectile Organelles: Food vacuoles.
  • B. Mitosis, Meiosis and Life History
    • Mitosis: Closed (text with tooltip) Mitosis is closed when the segregation of daughter chromosomes occurs within the bounds of the nuclear membrane (the nuclear membrane does not break down). with internal spindle (text with tooltip) An intranuclear spindle elaborates within the nuclear membrane of an organism with closed mitosis. .
    • Meiosis: Probably occurs, but it has not been described.
    • Sexual Reproduction and Life History: Poorly understood; life histories have been characterized for very few species.
  • C. Ecology: Plankters; mostly marine, some freshwater.
LITERATURE CITED

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By Jack R. Holt. Last revised: 03/07/2013
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