Centrohelida Kühn, 1926

 

Key to the genera (should be revised):

 

1

Without siliceous elements in periplasts

2

-

Periplasts with siliceous elements

3

2

Cell surface is naked

Oxnerella

-

Cell surface is covered by a mucous coat and may bear tangential or radial organic spicules

3

3

Organic spicules absent

Chlamydaster

-

Organic spicules present

4

4

Spicules tangential

Sphaerastrum

-

Spicules radial

Heterophrys

5

Periplast comprised of tangential elements only

6

-

Periplast with tangential plate scales and radial elements

9

6

Periplast comprised of tangential rod-like spicules

Parasphaerastrum

-

Periplast comprised of elliptical or spindle-shaped plate-scales

7

7

All scales with a broad marginal rim

9

-

Two types of plate scales, both lacking broad marginal rim

Pseudoraphidiophrys

8

Scales with smooth or reticulate texture

Polyplacocystis

-

Plate scales with radial slits

Raphidiophrys

9

Radial elements tube-shaped, trumpet-shaped or funnel-shaped

10

-

Radial elements spine-like; plate scales without broad marginal rim

11

10

With one type of funnel-shaped radial ele­ments; plate scales without broad marginal rim

Pseudoraphidocystis

-

Two types of radial elements: funnel-shaped and trumpet-shaped or tube-like; plate scales with broad marginal rim

Raphidocystis

11

Spicules are bilaterally symmetrical and consist of a shaft and a base formed as a continuation of a membranous flange to the shaft

12

-

picules consist of a shaft and a discrete baseplate

13

12

The 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 stalk

Pterocystis

13

Spicule base-plates are heart-shaped; the shafts attach centrically

Choanocystis

-

Base plates of spicule are circular; shafts attach centrally

Acanthocystis

 

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