Desmothoracid

Desmothoracida
Blaschka glass model of Clathrulina elegans
Scientific classification
Domain:	Eukaryota
(unranked):	SAR
(unranked):	Rhizaria
Phylum:	Cercozoa[1]
Class:	Granofilosea[2]
Order:	Desmothoracida Hertwig & Lesser, 1874
Family:	Clathrulinidae Claus, 1874
Genera
see text

Order Desmothoracida, the desmothoracids, are a group of heliozoan protists, usually sessile and found in freshwater environments. The 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.

Reproduction takes place by the budding off of small motile cells, usually with two flagella. Later these are lost, and the pseudopods and lorica are formed. Typically, a single lengthened pseudopod will secrete a hollow stalk that attaches the cell to the substrate. The form of the flagella, the tubular cristae within the mitochondria, and other characters have led to the suggestion that the desmothoracids belong among what is now the Cercozoa. This was later confirmed by genetic studies.

As of the year 2000, the order Desmothoracida contained five genera with a total of 10 species.^[3]

• Genus Clathrulina
  • Clathrulina elegans
  • Clathrulina smaragdea
• Genus Hedriocystis
  • Hedriocystis pellucida
  • Hedriocystis minor
  • Hedriocystis zhadani
• Genus Penardiophrys
  • Penardiophrys reticulata
  • Penardiophrys spinifera
• Genus Cienkowskya
  • Cienkowskya mereschkovckii
  • Cienkowskya brachypous
• Genus Actinosphaeridium
  • Actinosphaeridium pedatus

Notes

1. Nikolaev, S. I.; et al. (May 2004). "The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes". Proc. Natl. Acad. Sci. U.S.A. 101 (21): 8066–71. doi:10.1073/pnas.0308602101. PMC 419558. PMID 15148395.
2. Bass, D.; et al. (February 2009). "Phylogeny of novel naked filose and reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea revised". Protist 160 (1): 75–109. doi:10.1016/j.protis.2008.07.002. PMID 18952499.
3. Mikrjukov, K. A. (2000). Taxonomy and phylogeny of Heliozoa. 1. The order Desmothoracida Hertwig et Lesser, 1874. Acta Protozoologica 39(2) 81-97.

References

• 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. doi:10.1023/B:DOBS.0000010322.33294.9f. PMID 14994549.