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