Phaeodarea
Encyclopedia
The Phaeodarea are a group of amoeboid
protist
s. 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 are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.
The term "Radiozoa" has been used to refer to radiolaria when Phaeodarea is explicitly excluded.
Phaeodarea produce hollow skeletons composed of amorphous silica and organic material, which rarely fossilize. The endoplasm
is divided by a cape with three openings, of which one gives rise to feeding pseudopod
s, and the others let through bundles of microtubule
s that support the axopods. Unlike true radiolarians, there are no cross-bridges between them. They also lack symbiotic algae, generally living below the photic zone
, and do not produce any strontium sulphate.
Amoeboid
Amoeboids are single-celled life-forms characterized by an irregular shape."Amoeboid" and "amœba" are often used interchangeably even by biologists, and especially refer to a creature moving by using pseudopodia. Most references to "amoebas" or "amoebae" are to amoeboids in general rather than to...
protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s. 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
Cercozoa
The Cercozoa are a group of protists. They are sometimes described as a kingdom.-Characteristics:The group includes 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...
. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.
The term "Radiozoa" has been used to refer to radiolaria when Phaeodarea is explicitly excluded.
Phaeodarea produce hollow skeletons composed of amorphous silica and organic material, which rarely fossilize. The endoplasm
Endoplasm
Endoplasm generally refers to the inner part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer layer of the cytoplasm....
is divided by a cape with three openings, of which one gives rise to feeding pseudopod
Pseudopod
Pseudopods or pseudopodia are temporary projections of eukaryotic cells. Cells that possess this faculty are generally referred to as amoeboids. Pseudopodia extend and contract by the reversible assembly of actin subunits into microfilaments...
s, and the others let through bundles of microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
s that support the axopods. Unlike true radiolarians, there are no cross-bridges between them. They also lack symbiotic algae, generally living below the photic zone
Photic zone
The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...
, and do not produce any strontium sulphate.