Nitzschia draveillensis Coste & Ricard 1980

Novis, Phil M., Braidwood, Jasmine & Kilroy, Cathy, 2012, Small diatoms (Bacillariophyta) in cultures from the Styx River, New Zealand, including descriptions of three new species, Phytotaxa 64 (1), pp. 11-45 : 23

Nitzschia draveillensis Coste & Ricard 1980 ( Figs 42–51 , 162 )

Frustules fusiform with extended rostrate poles, 47.0–63.0 µm long, 3.4–4.5 µm wide in valve view; sometimes slightly constricted at midpoint at one or both margins. Living cells containing 2 plate-like parietal chloroplasts, one towards each pole ( Fig. 42 ). Striae very fine, transverse, 69–72 in 10 µm, not visible in LM. Raphe system marginal, fibulate, 21–23 fibulae in 10 µm, but with two median fibulae more widely spaced; raphe on opposite margins of the two valves. Central raphe endings occurring between median fibulae ( Fig. 51 , visualised in TEM; not discerned either in LM or SEM).

References: — Coste & Ricard (1980) p. 190, figs 70, 73, 74; Krammer & Lange-Bertalot (1988) p. 123–124, fig. 85: 5–6.

Specimens examined: —CHR618409! (cleaned frustules from cultured strain LCR-S:37:3).

Distribution: —There are two unpublished records of this species from New Zealand, from Lake Moeraki, 17 December 2002 (2 frustules seen) and Lake Wahapo, 16 December 2002 (1 frustule seen). The species is not commonly reported world-wide. It appeared in culture from the Styx at site 6.

Molecular data: —There were no close matches to the 18S sequence of this strain; the closest was N. pusilla Grunow 1862 clone NIPU1, isolated from the Rollingerbaach River, Luxembourg (p-distance = 0.020). The Styx strain was placed alone on a long branch in the Bayesian analysis, without any robustly resolved relationships ( Fig. 162 ). The MPB analysis placed it sister to N. acicularis (Kütz.) Smith 1853 , but with low bootstrap support (56%). The length of the Styx fragment was 1168 bp in an overall dataset 1707 bp long, containing 91 variable sites (39 parsimony informative, 27 occurring within the Styx fragment).

Observations: — Coste & Ricard (1980) did not specifically describe the position of the raphe canal on the two valves of N. draveillensis , although they stated that the differences between this and N. acicularis were the occurrence of median fibulae, very delicate striae with quadrangular areolae, and very long extremities in N. draveillensis . We take this to imply that the raphe canals are on opposite sides of the valves in both species, which agrees with our observations here. We observed both rectangular and quadrangular areolae on the same valve in our specimens, but the striae and fibulae densities are close to Coste & Ricard’s observations (55–64 and 19–21 in 10 µm respectively). Our specimens were not as long as theirs (up to 110 µm). We note that this species and N. acicularis are very easily confused, the most important difference being the presence of the more widely spaced median fibulae and central raphe endings in N. draveillensis . Given the ease with which these features can be overlooked, we wonder how reliably the distribution of these two species can be known, and whether N. acicularis actually occurs in New Zealand. Molecular data suggest that the two species are not very close relatives.

Figures

FIGURE 162. Bayesian phylogenies of Nitzschia strains from the Styx River, for rbcL (left) and 18S rDNA (right). Support numbers above branches are Bayesian posterior probabilities / Maximum Parsimony bootstrap values. Scale bar = 0.1 subsitutions/site. See text for substitution models and description of data sets.

FIGURE 42–51. Nitzschia dravaillensis, strain LCR-S:37:3, CHR618409. Scales: Fig. 42, 10 µm; Fig. 49, 5 µm (use for Figs 43–49); Fig. 50, 1 µm; Fig. 51, 0.5 µm. Fig. 42. Live cells viewed by LM. Figs 43–49. Cleaned frustules viewed by LM, showing size variation, and median fibulae visible in 43. Fig. 50. SEM of cleaned frustule showing raphe canals on opposite margins, and median fibulae. Fig. 51. TEM of cleaned frustule showing median fibulae and raphe with central termini.