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Family Hyalospheniidae Schultze, 1877 emend. Kosakyan and Lara, 2012

Diagnosis: The test is rigid, colorless or yellowish-brown, flask-shaped, oval or pyriform, dorso-ventrally compressed. The shell is either entirely self secreted (e.g. Hyalosphenia) composed of an organic matrix, or with addition of self secreted siliceous plates (Quadrulella) or recycled shell plates of small euglyphids or other similar material such as diatom frustules incorporated in the test. The pseudostome is terminal and bordered by a thin organic collar.

Key to the genera
1
Test composed of different materials
2
Test chitinoid, clear, completely organic, non–areolar
4
2
Test composed of self secreted quadratic plates
3
Test composed either of recycled shell plates of small euglyphids or other similar material such as diatom frustules incorporated in the test (plates sometimes covered by very thick organic layer giving the impression of a chitinoid, clear, organic and non structured test) or composed of agglutinated particles as in genus Difflugia
5
3
Lateral margins distinctly compressed giving the impression of a thick and wide hollow keel. Because of this, the test is elongated elliptical with the pointed end in the profile.
Test without lateral compressed margins
4
Test oval elongated, pyriform, flask shaped sometimes with an elongated neck or wedge shaped, totally transparent without structure
Test pyriform, with a lateral indentation at each side, test often organic, totally hyaline, without structure, but sometimes with a (probably self secreted) rough granulated structure (visible by SEM)
5
Test with two lateral horns, pointing towards the posterior part of the test, either free or connected to the main part of the test by a lateral keel surrounding the posterior part of the test.
Test without lateral horns
6
6
Test at the base of the neck with two distinct lateral depressions with two large invaginated pores (2-5 μm) situated on each side, which are connected by internal tubes
7
Test lacking pores in depressions connected by internal tube.
8
5
Test flask-shaped, with an elongated neck. Internal side of neck with pointed protuberances visible in LM as lines of points
Test lacking pointed protuberances in the internal side of the neck
8
Test with distinct keel
9
Test without keel
10
9
Test with a flat keel
Test with a hollow tuberous keel
10
Test with conspicuous elongated neck
11
Neck not elongated
12
11
Neck deeply constricted at the junction with the main body of the test
No constriction at the base of the neck
12
Test flask-shaped, oval-elongated, pyriform, neck either absent, short or if long tapering toward the aperture and never clearly separated from the base of the test
13
Test elongated-pyriform, with a distinct neck, lateral margins (that can be straight or wavy) tapering towards the aperture
13
Test flask-shaped, oval-elongated, pyriform, neck either absent, short or if long tapering toward the aperture and never clearly separated from the base of the test
Pseudostome strongly convex

References: Kosakyan, A., Heger, T.J., Leander, B.S., Todorov, M., Mitchell, E.A.D. and Lara, E.: COI Barcoding of Nebelid Testate Amoebae (Amoebozoa: Arcellinida): Extensive Cryptic Diversity and Redefinition of the Hyalospheniidae Schultze – Protist 163, issue 3, 415-434, 2012

Kosakyan, A., Gomaa, F., Lara, E. and Lahr, D.J.G. : Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae – European Journal of Protistology, 2016

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