Algae World: Sellaphora

Diversity: the 'bacillum group'

Sellaphora: bacillum group

Description

Members of the 'bacillum group' generally have a linear to elliptical outline, with broadly rounded or acute poles. They may be very slightly constricted at the centre. Polar bars are present (blue arrow). The axial area is narrow or of moderate width and the central area is rounded, with well defined edges. The axial area is depressed below the rest of the valve face and covered by a narrow conopeum ('canopy'), which is attached to the raphe-sternum on one side and with a free margin on the other side (Sims & Paddock 1979). The conopeum thus creates a narrow longitudinal chamber or canal on the outside of the valve, next to the raphe system. The effect in the LM is to create two closely associated longitudinal lines running parallel to the raphe slits (red arrows) along the whole length of the valve, becoming further apart where they enclose the central raphe endings.

The polar bars and narrow axial area separate the 'bacillum group' from the 'americana group'. The shape of the central area, full-length conopea (creating canals running from pole to pole) and the simple valve outline separate the 'bacillum group' from the 'pupula group'.

Species list

References

Sims, P.A. & Paddock, T.B.B. (1979). Observations and comments on some prominent morphological features of naviculoid genera. Nova Hedwigia, Beiheft 64: 169–191.

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