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Desmothoracid

A group of heliozoan protists, usually sessile and found in freshwater environments. The adult is a spherical cell surrounded by a perforated organic lorica, or shell, with many radial pseudopods projecting through the holes to capture food. These are supported by small bundles of microtubules that arise near a point on the nuclear membrane; unlike other heliozoans, the microtubules are not in any regular geometric array, and there does not appear to be a microtubule organizing center to speak of. The mitochondria have tubular cristae, and there is no distinction between the outer and inner cytoplasm.

There are three genera in the group: Clathrulina[?], Hedriocystis[?], and Cienkowskya[?]. Monomastigocystis appears to be a synonym for the last. The cells are usually 10-20 μm in diameter, with an envelope that may be a couple times that size. Reproduction is 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 attaches the adult to the substrate.



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