Centrohelida Kühn, 1926

Key to the genera (should be revised):

1Without siliceous elements in periplasts2
Periplasts with siliceous elements3
2Cell surface is nakedOxnerella
Cell surface is covered by a mucous coat and may bear tangential or radial organic spicules3
3Organic spicules absentChlamydaster
Organic spicules present4
4Spicules tangentialSphaerastrum
Spicules radialHeterophrys
5Periplast comprised of tangential elements only6
Periplast with tangential plate scales and radial elements9
6Periplast comprised of tangential rod-like spiculesParasphaerastrum
Periplast comprised of elliptical or spindle-shaped plate-scales7
7All scales with a broad marginal rim9
Two types of plate scales, both lacking broad marginal rimPseudoraphidiophrys
8Scales with smooth or reticulate textureRaphidocystis
Plate scales with radial slitsRaphidiophrys
9Radial elements tube-shaped, trumpet-shaped or funnel-shaped10
Radial elements spine-like; plate scales without broad marginal rim11
10With one type of funnel-shaped radial ele­ments; plate scales without broad marginal rimPseudoraphidocystis
Two types of radial elements: funnel-shaped and trumpet-shaped or tube-like; plate scales with broad marginal rimRaphidocystis
11Spicules are bilaterally symmetrical and consist of a shaft and a base formed as a continuation of a membranous flange to the shaft12
picules consist of a shaft and a discrete baseplate13
12The membranous base continues as two lateral wings extending along the shaft, and a further basal wing forms the base of the spicule extending perpendicularly to the shaft and lateral wingsshaft Echinocystis
Without well-developed basal wing; spicules often with stalkPterocystis
13Spicule base-plates are heart-shaped; the shafts attach centricallyChoanocystis
Base plates of spicule are circular; shafts attach centrallyAcanthocystis

This key comes from The Illustrated Guide (2000), which I was one of the authors.

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