Algae World: Sellaphora

Analysis

Does this species belong to Sellaphora?

Probably, but this needs confirmation. So far, there are no data on protoplast or auxosporulation, nor DNA sequence data.

Affinities

If S. macedonica does belong to Sellaphora, then Gestalt morphology suggests it might belong in the 'laevissima' group, as implied by the differential diagnoses given by Levkov et al.: S. macedonica is a moderate-sized species with a linear or linear-lanceolate outline, resembling S. laevissima. However, no morphological synapomorphies are known for the laevissima group and DNA sequence data are essential for classification.

But close inspection of the LM figures provided by Levkov et al. (pl. 106, figs 1-7) suggests that polar bars may be present at the valve poles, although these are not mentioned in the text. This is supported by the external SEM views (pl. 108, figs 3, 4), which appear to show interruptions in the striae corresponding to where bars would be internally if present. Polar bars are a synapomorphy for the 'pupula-bacillum' clade. No internal SEM views of S. macedonica have yet been given.

Morphological data

The original description represents all that has been published thus far concerning variation in this species. The micrographs provided by Levkov et al. to illustrate the species are of high quality. There is no suggestion from the micrographs that S. macedonica is heterogeneous: the variation shown is entirely consistent with what one would expect to occur during size reduction.

The sexual phase was not observed and, as in other such cases, the size range given in the original description probably underestimates the full range for the species. The stria density seems to be more constant in the valves illustrated than is stated in the description; unfortunately, plate 106, illustrating the 'holotype specimen' and six other examples by LM, does not contain a scale bar. Judging by the LM and SEM figures provided by Levkov et al., the poles could be described as subacute, rather than 'broadly rounded' as stated in the description.

The original description indicates that there are depressions externally, alongside the raphe system. The SEM figures (pl. 108, figs 3, 4) show that these are slight indentations along the proximal parts (containing the first one to three poroids) of each stria, rather than the longitudinal grooves present in some other Sellaphora species.

Distribution

It is too early to say whether this species is restricted to Lake Ohrid or found more widely. Basing records on morphological comparisons is likely to be unsafe, although the subacute poles and small central area are unusual among linear-valved members of the 'pupula-bacillum' clade.

Typification

Levkov et al. not only indicate a holotype slide but also specify (via an image) a specimen on the slide, though its location on the slide has not been published.