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Hyalosphenia elegans
Hyalosphenia elegans

Genus Hyalosphenia (Stein, 1857) Schulze 1877

Diagnosis: Test rounded, ovoid or elongated elliptical or flask shaped, laterally compressed, aperture variable from linear to strongly curved, with or without thickened lip. Test hyaline or slightly yellowish, with a smooth organic surface (exception: Hyalosphenia punctata which has a punctuated surface).
Type species: Hyalosphenia cuneata (Stein) Schulze. 20 species are considered as valid, among which many are problematic and need molecular data to confirm their position within the genus.

Key to the species
1
Test with a distinct neck
2
Test without distinct neck, rounded, ovoid, or elongated elliptical
9
2
Neck long, test flask- or bottle-shaped
3
Neck very short
6
3
Lateral margin of test not smooth
4
Lateral margin of test smooth or slightly wavy
5
4
Main part of test with round to oval depressions, giving the outline a inrregularwavy apprearance, L=(68)85-110(130)μm, B=40-65 μm, aperture curved, with a well-developed 15-20 μm wide organic collar
H. elegans
Round to oval depressions not limited to the main part of the test but extending toward the neck
H. insecta
5
Lateral margin of the test very smooth, neck widening near aperture, L=84μm, B=49 μm
H. jirovici
Lateral margin of the test smooth or slightly wavy, neck cylindrical and not widening near the pseudostome,dimensions as H. elegans
H. elegans var. cylindricolis
6
Neck very short, test oval-rounded
7
Neck longer, test more elongated
8
7
Smaller species, very rounded (L/B=14-17/12-16 μm. Aperture is 6.5-7.7 μm wide, ellipsoid, in the side view curved inside)
H. inconspicua
Larger species, L=65-70 μm, B=50 μm, pseudostome 23-25 μm wide
H. humicola
8
Smaller species, L<45 μm, L =42μm, B=22 μm, pseudostome narrow 5 μm wide, shape described as “resembling the piston of a small automotive bulb”
H. lucerna
Larger species, L>45 μm (test wide ovoid L =130-180μm, B = 90-140 μm, including the keel
H. ovalis
9
Pseudostome thickened
17
Pseudostome not thickened
10
10
Test very elongated ellipsoid
16
Test ovoid
11
11
Test very wide ovoid, length almost equalt to the breadth, pseudostome linear, L=40-42 μm, B=28-32 μm, aperture 28-32 μm
H. platystoma
Test narrower, lateral sides gradually tapering toward the pseudostome, which is strongly or slightly curved
12
12
Test composed of small organic building units, similar to Arcella
H. punctata
Test totally smooth, without any structure
13
13
Smaller species, L< 90 μm
15
Larger species L> 90 μm
14
14
Mixotrophic species, always with zoochlorellae. L =90-175μm, B=60-155 μm, aperture 30-40 μm wide, slightly curved or linear
H. papilio
Pseudostome narrower, similar in shape to that of Nebela militaris or N. collaris s.l.
H. papilio var. stenostoma
15
Tiny lateral keel present, L = 52-76μm, B=44-60 μm
H. cuneata
Lateral keel absent, but in side view the aboral of the test is slightly pointed, L=45μm, B=60 μm
H. angulata
16
L<200 μm
H. penardi
L >200 μm
H. gigantea
17
→Pseudostome clearly thickened, L=40-65μm, B=23-40 μm
H. schoutedeni
Pseudostome not clearly thickened
18
18
Smaller species L<45 μm
19
Larger species L>45 μm
20
19
Test ovoid, elliptical in side view. L=26-43 μm, B=16-27μm, aperture 13 μm wide
H. minuta
Test more rounded, L =20μm, B=17 μm
H. schoutedeni var. rotundata
20
Test more elongated, L/B ratio=3 or more, L=107-115 μm, B=31-36 μm
H. tamdaensis
L/B ratio always < 2, L=45-87 μm, B=30-53μm
H. subflava

Key from Kosakyan, A.

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