Hyalosphenia elegans
Genus Hyalosphenia (Stein, 1857) Schulze 1877
Diagnosis: Shell rounded, ovoid or elongated elliptical or flask shaped, laterally compressed, aperture variable from linear to strongly curved, with or without thickened lip. Shell 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
Shell with a distinct neck
2
–
Shell 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
Shell very elongated ellipsoid
16
–
Shell ovoid
11
11
Shell 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
–
Shell narrower, lateral sides gradually tapering toward the pseudostome, which is strongly or slightly curved
12
12
Shell composed of small organic building units, similar to Arcella
H. punctata
–
Shell 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
Shell ovoid, elliptical in side view. L=26-43 μm, B=16-27μm, aperture 13 μm wide
H. minuta
–
Shell more rounded, L =20μm, B=17 μm
H. schoutedeni var. rotundata
20
Shell 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.