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Key to Cyclopyxis species
1 Pseudostome star-shaped 2
Pseudostome circular 3
Pseudostome cross-shaped

C. crucistoma

2 Diameter of the test 335-400 microns

C. stellata

Diameter of the test 120-130 microns

С. grospietschi

3 Diameter of the test < 80 microns 4
Diameter of the test > 80 microns 9
4 Test completely covered with diatoms
C. bacillifera
Test covered with quartz particles 5
5 Test flattened, height/diam. ratio < 0.55 6
Test hemispherical (height/diam. > 0.55) 7
Test conical
C. tronconica
6 Diameter 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

7 Height of test equal or larger than diameter 8
Height of test less than its diameter
C. eurystoma
8 Pseudostome strongly concave C. eurystoma sinuosa
Pseudostome slightly concave C. eurystoma alta
9 Test hemispherical, pseudostome relatively large, > 1/3 test diameter 10
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

10 Test flattened 11
Pseudostome circular 13
11 The diameter of the mouth is about half the diameter of the shell 12
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 microns C. eurystoma sinuosa
13 Diameter 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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