Desmothoracid

Desmothoracida
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Blaschka glass model of Clathrulina elegans
Scientific classification
Domain:	Eukaryota
(unranked):	SAR
(unranked):	Rhizaria
Phylum:	Cercozoa
Class:	Granofilosea
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.

• 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