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Key to Cyclopyxis species
1Pseudostome star-shaped2
Pseudostome circular3
Pseudostome cross-shaped

C. crucistoma

2Diameter of the test 335-400 microns

C. stellata

Diameter of the test 120-130 microns

С. grospietschi

3Diameter of the test < 80 microns4
Diameter of the test > 80 microns9
4Test completely covered with diatoms
C. bacillifera
Test covered with quartz particles5
5Test flattened, height/diam. ratio < 0.556
Test hemispherical (height/diam. > 0.55)7
Test conical
C. tronconica
6Diameter of pseudostome > 0.65 diameter of the test
C. plana
 
Diameter of pseudostome is 0.5-0.6 diameter of the test

C. amplecta

Diameter of pseudostome < 0.5 diameter of the test

C. aplanata microstoma

7Height of test equal or larger than diameter8
Height of test less than its diameter
C. eurystoma
8Pseudostome strongly concaveC. eurystoma sinuosa
Pseudostome slightly concaveC. eurystoma alta
9Test hemispherical, pseudostome relatively large, > 1/3 test diameter8
Lateral sides of the test almost parallel; dorsal side in lateral view somewhat flattened, with large mineral particles often protruding from its sides; small mineral particles around the deep mouth

C. kahli

8Test flattened11
Pseudostome circular13
11The diameter of the mouth is about half the diameter of the shell12
Diameter of mouth is not more than 1/4 of the diameter of the shell

C. aplanata microstoma

12
Diameter of the test 180-28 microns
С. aplanata
Diameter of the shell 130 micronsC. eurystoma sinuosa
13Diameter of the test 80-18 microns; pseudostome up to 1/2 the diameter of the test; surrounded by small, often shiny mineral particles, why it seems finely toothed

C. arcelloides

Diameter of the test 330-380 microns; pseudostome > 1/2 of test diameter

C. penardi

 

This key was published by Mazei and Tsyganov in 2006, Moskou, in Russian. I’ve translated it and modified it by adding some species.

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