Navicula veneta Kützing 1844

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 : 31-32

Navicula veneta Kützing 1844 ( Figs 97–111 , 165 )

Frustules linear-lanceolate in valve view, 4.7–5.5 µm wide, 19.2–19.7 µm long, with broadly subrostrate apices, biraphid. Living cells containing 2 plate-like parietal chloroplasts, one each side of the girdle ( Fig. 97 ), a cytoplasmic bridge, and two volutin granules. Areolae elongate and longitudinally aligned; striae thus uniseriate and lineolate, 17 in 10 µm, weakly radiate around central area to transverse (to slightly convergent) at valve poles ( Figs 110, 111 ). Central area widened, with 2–3 shorter striae. Raphe straight, with slightly expanded, strongly hooked central endings forming a barbed protrusion ( Figs 106–109 ), and polar endings hook-shaped over the valve apices.

References:— Krammer & Lange-Bertalot (1986), p. 104, figs 32: 1–4; Cox (1995), p. 109, figs 64–67; Moro et al. (2010), p. 211–212, figs 1–4; Pouličková et al. (2010), table 1, fig 1B.

Specimens examined: —CHR618416 (cleaned frustules made from culture LCR-S:2:2:1); CHR618417 (cleaned frustules made from culture LCR-S:34:3).

Distribution: —The species is regarded as common and cosmopolitan ( Pouličková et al. 2010), and is well known from New Zealand. It was found at 2 sites in the Styx (1 and 10).

Molecular data: —The Styx strain of N. veneta shared identical 18S sequences with other strains of N. veneta: NCB , AT-108Gel01, AT-110Gel19, and AT-117Gel20b (there are small differences between these sequences, but not over the region sequenced in the Styx strain). These strains were isolated from Europe (the first from thermal mud in Italy, the others from rivers near Hamburg, Germany). The Styx strain formed a robust clade with these strains of N. veneta in both Bayesian and MPB analyses ( Fig. 165 ). The length of the 18S fragment was 1216 bp in an overall dataset of 1822 bp with 147 variable sites (91 parsimony informative, 52 occurring in the Styx fragment). The model selected by BIC and implemented in the Bayesian analysis was T93+G+I.

Observations: —We concur with Moro et al. (2010) and Pouličková et al. (2010) that subsuming N. veneta into N. cryptocephala as a variety is not justified, given that the two species were well separated by robust splits in our analyses. The Styx specimens conform well to published descriptions of N. veneta ( Krammer & Lange-Bertalot 1986, Moro et al. 2010) with one exception: the central raphe endings at the pores are strongly hooked. This is shared by one specimen illustrated by Cox (1995) from a brackish site in Kent, UK. To our knowledge this has not been found in any other specimens of N. veneta . All specimens examined possessed this feature, including individuals recovered from 2 sites in the Styx and independently cultured; thus the feature seems stable. There appears to be significant variation in the central raphe endings of N. veneta ; for instance, they are somewhat expanded in strain ETS-07 ( Moro et al. 2010) compared to our findings. It may be possible to use this as a means of identifying subspecific taxa, but this would require a detailed SEM-level examination of many collections. The isolation of this species from thermal mud by Moro et al. (2010) suggests that its habitat preferences are very broad.

Figures

FIGURE 165. Bayesian phylogenies of Navicula, Sellaphora, and Eolimna strains from the Styx River, for 18S rDNA (left) and rbcL (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 97–111. Navicula veneta, strain LCR-S:2:2:1, CHR618416. Scales: Fig 97, 10 µm; Fig. 98, 5 µm (use for Figs 98–104); Fig. 109, 1 µm (use for Figs 106–109), all others 1 µm. Fig. 97. Live cells viewed by LM, showing paired parietal plastids close against valve margins. Fig. 98–104. Cleaned frustules viewed by LM (girdle view in Fig. 104). Figs 105–111. SEM of cleaned frustules. Fig. 105, whole frustule, showing elongated, longitudinally aligned areolae; Figs 106–109, widened central area of four valves, showing hooked central raphe termini; Figs 110, 111, valve apices showing hooked raphe termini and pattern of areolae.