Desmothoracid

The desmothoracids are a group of heliozoan 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 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, there does not appear to be a microtubule organizing center, and there is no distinction between the outer and inner cytoplasm.

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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.

References

• K.A. Mikrjukov (2000). "Taxonomy and Phylogeny of Heliozoa. I. Desmothoracids". Acta Protozoologica 39: 81-97.
• Nikolaev, S.I. et al. (2003). "Genetic Relationships between Desmothoracid Heliozoa and Gymnophryid Amoebas as Evidenced by Comparison of 18S rRNA Genes". Doklady Biological Sciences 393: 553-556.