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Centrohelida Kühn, 1926

Key to the genera:

1

Cell naked or surrounded by organic elements

2

Cell surrounded by siliceous elements

5

2

Cell surface naked; axopodia with prominent extrusomes and normally stretched across the substratum.

Cell surrounded by a mucous layer; axopodia not with prominent extrusomes and not stretched across the substratum.

 

3

3

Mucous layer embedded with organic spicules

4

Mucous layer fimbriated, without organic spicules

4

Spicules mainly tangentially arranged

Spicules radially arranged 

5

Cell covered by tangentially and loosely arranged plate-scales; these plate-scales are elliptical to spindle-shaped or rod-like

6

Cell with two types of scales: tangentially arranged elliptical plate-scales and radially arranged (spine-)scales

10

6

Scales are slightly curved solid needles or rods 

Scales are broadly elliptical to spindle-shaped, but never rod-shaped

                                         

 

 

 

7

7

Cell with one type of plate-scales; spindle-shaped plates may occur. 

8

Cell with two types of plate-scales, both having a different morphology

 

9

8

Plate-scales monolayered, with a hollow inflected margin and with a smooth or reticulate texture.  

Plate-scales consisting of an upper and lower plate connected by internal radial septa. 

9

Plate-scales of the inner layer are flattened, simple in structure, usually ornamented with an axial rib.

Plate-scales of the inner layer small. without a hollow marginal rim; plate-scales of the outer layer larger , with a well-developed sternum and radiating ribs. The base of the sternum may be expanded and concave to create a velum-like extension of the scale.

10

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

11

Radial elements spine-like

12

11

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

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

12

Spine-scales consist of a shaft and two lateral wings, resembling a spoon, spade or feather

13

Spine-scales consist of a shaft and a discrete circular or heart-shaped base-plate

14

13

Radial spine-scales consist of a shaft and a thin, membranous basal region which may extend along the shaft and may form a stalk-like protrusion at the base of the spicule 

R. erinaceoides

The radial scales have a shaft with two lateral wings extending along it, and a basal wing oriented perpendicular to the lateral ones

Pterocystis

14

Base-plates of spine-scales are heart-shaped; the shafts attach centrally

Base-plates of spine-scales are circular; shafts attach centrally

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