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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 8
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

8 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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