Desmothoracid
Encyclopedia
The desmothoracids are a group of heliozoa
n protists, usually sessile and found in freshwater environments. Each adult is a spherical cell around 10-20 μm in diameter surrounded by a perforated organic lorica or shell, with many radial pseudopod
s projecting through the holes to capture food. These are supported by small bundles of microtubule
s that arise near a point on the nuclear membrane. Unlike other heliozoans, the microtubules are not in any regular geometric array, there does not appear to be a microtubule organizing center, and there is no distinction between the outer and inner cytoplasm.
Reproduction takes place by the budding off of small motile cells, usually with two flagella. Later these are lost, and pseudopods and a lorica are formed. Typically a single lengthened pseudopod will secrete a hollow stalk that attached the adult to the substrate. The form of the flagella, the tubular cristae within the mitochondria
, and other characters led to the suggestion that the desmothoracids belong among what is now the Cercozoa
, which has now been confirmed by genetic studies.
Heliozoa
Heliozoa are phagotrophs. They are roughly spherical amoeboids with many stiff, microtubule-supported projections called axopods radiating outward from the cell surface. These give them the characteristic sun-like appearance for which they are named, and are variously used for capturing food,...
n protists, usually sessile and found in freshwater environments. Each adult is a spherical cell around 10-20 μm in diameter surrounded by a perforated organic lorica or shell, with many radial 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 projecting through the holes to capture food. These are supported by small 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 arise near a point on the nuclear membrane. Unlike other heliozoans, the microtubules are not in any regular geometric array, there does not appear to be a microtubule organizing center, and there is no distinction between the outer and inner cytoplasm.
Reproduction takes place by the budding off of small motile cells, usually with two flagella. Later these are lost, and pseudopods and a lorica are formed. Typically a single lengthened pseudopod will secrete a hollow stalk that attached the adult to the substrate. The form of the flagella, the tubular cristae within the mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
, and other characters led to the suggestion that the desmothoracids belong among what is now 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...
, which has now been confirmed by genetic studies.