Algae World: Sellaphora ohridana

Sellaphora ohridana

Original description

Sellaphora ohridana Levkov & Krstic in Levkov, Krstic, Metzeltin & Nakov

Z. Levkov, S. Krstic, D. Metzeltin & T. Nakov (2007). Diatoms of Lakes Prespa and Ohrid. In: H. Lange-Bertalot (ed.) Iconographia Diatomologica, vol. 16, Biogeography – Ecology – Taxonomy, pp. 1–611. A.R.G. Gantner, Ruggell, Liechtenstein.

pp. 120, 121; pl. 103, figs 1-14; pl. 104, figs 1-6

Description

"Valves linear to linear-elliptic with broadly rounded ends, length 20-61 µm, width 10-12 µm. Raphe is filiform with large central pores, expanded and slightly deflected to primary valve side. Terminal raphe fissures prolonged, curved to the limbus. Axial area is moderately wide, central area large, elliptical to slightly asymmetrical. Terminal area distinct. Narrow depressions flanking the raphe sternum. Striae are radiate in the middle, 14- 16/10 µm, becoming convergent at the ends. Areolae can not be resolved in LM, 48-52/10 µm.

"Valvae lineares ad lineari-ellipticae apicibus late rotundatis, longae 20-61 µm, latae 10-12 µm. Raphe filiformis poris centralibus distinctis, deflexis ad latus primum valvae. Extrema raphis terminalia elongata curvata ad limbum valvae. Area axialis modice lata, area centralis lata, elliptica vel paulo asymmetrica. Area terminalis distincta. Depressiones angustae utroque ad sternum. Striae radiantes in media parte 14-16/10 µm, convergentes ad apices. Areolae non discernandae in LM, 48-52/10 µm."

Diagnostic information

"Main diagnostic characters: valve width, striae and areolae density."

"... closely related to S. bacillum (Ehrenberg) D.G. Mann, but is differs by higher stria density (14-16/10 µm versus 12-14/10 µm) and striae orientation. From S. sublinearis Metzeltin & Lange-Bertalot it could be distinguished by valve width (10-12 µm versus 8-9 µm), stria density (14-16/10 µm versus 22-24/10 µm) and areola density (48-52/10 µm versus 28-30/10 µm)."

Type data

Holotype: slide DCIBS (Diatom Collection, Faculty of Natural Sciences, Skopje) 000759, holotype specimen pl. 103, fig. 5.
Isotypes: slides DCIBS 000757, 000758.
Type material: St Naum springs, Lake Ohrid, sand. Collected 25 April 2003. Accession No. 000532.

Etymology: the epithet refers to the lake where this species was first observed.

Distribution: "until now, this species is known only from Lake Ohrid."

Analysis

Does this species belong to Sellaphora?

Yes, through possession of a morphology linking it to particular species known to belong to Sellaphora, in the 'bacillum' group'; S. ohridana possesses polar bars. However, so far, there are no data on protoplast or auxosporulation, nor DNA sequence data.

Affinities

Valve morphology suggests that this belongs to the 'bacillum' group. Like S. bacillum, it possesses a narrow conopeum externally.

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 a slight suggestion from the micrographs of heterogeneity among the valves illustrated: figs 3 and 5 seem to show more rounded, elliptical valves than in the other 11 figures, although this could be because thecae or frustules are shown, rather than valves. Apart from this, the variation shown is entirely consistent with what one would expect to occur during size reduction. Unfortunately, no scale bar was included on the LM figures (pl. 103, figs 1-14).

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, though possibly not by very much, judging by the proportions and shape of the longest specimen shown (pl. 103, fig. 1). The poles are rather narrower and the valves more lanceolate than is usually illustrated for S. bacillum and could be described as broadly subacute in the smallest valves (figs 7-13), rather than 'broadly rounded'..

The original description does not mention an interior depression on the apical side of the helicoglossa, but this is shown and labelled on pl. 104, fig. 4. This feature is also present in several other Sellaphora species, including S. krsticii, described as a new species in the same volume of Iconographia diatomologica.

A narrow non-porous conopeum is shown in pl. 104, figs 1-3. The internal central raphe endings are bent towards the primary side as in other Sellaphora species (pl. 104, fig. 6). The terminal fissures curve off smoothly towards the secondary side (pl. 104, fig. 1).

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.

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. The particular specimen chosen (pl. 103, fig. 5) is not like all of the others, as noted above.

Algae World: Sellaphora