Eolimna krummensis, Novis & Braidwood & Kilroy, 2012

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 : 33-34

Family Sellaphoraceae

Eolimna krummensis sp. nov. P.M. Novis, J. Braidwood & C. Kilroy ( Figs 112–129 , 165 )

Frustules pennate, biraphid, elliptic-lanceolate in valve view, 2.6–3.5 µm wide, 7.6–9.4 µm long, with rounded ends. Living cells containing 2 narrow, parietal platelike chloroplasts, closely adhering to the inner valve margins ( Fig. 112 ). Striae radiate and slightly curved towards the central area, 34–36(–39) in 10 µm, uniseriate, roundish areolae decreasing in size towards the valve margin ( Fig. 121 ). Central area widened, bordered by (3–)4 shortened striae on each margin of the valve. Raphe straight, widened at central termini, curved to the secondary valve side at valve apices.

Type:— NEW ZEALAND: Canterbury: Smacks Creek (lat. 43°27.637, long. 172°35.406), periphyton, P.M. Novis and J. Braidwood, 4 November 2009 ( CHR618418 !; cleaned frustules from cultured strain LCR-S:10:2:1) .

Distribution: —Currently 2 localities are known for this species: the Styx River (sites 2 and 3), New Zealand, and Krumm See, Germany, where strain AT-199Gel01 was isolated from lake phytoplankton. The latter strain does not appear to have been described in the literature, but shares an almost identical DNA sequence (see below).

Etymology: —the species name comes from Krumm See, the site of isolation of strain AT-199Gel01 in Genbank (see below).

Molecular data: —The closest match to the rbc L sequence of the Styx strain was Eolimna krummensis (as Mayamaea atomus (Kütz.) Lange-Bert. in Genbank) strain AT-199Gel01 (p-distance = 0.003). In both analyses the Styx strain formed a robust monophyletic group with this strain, Eolimna minima (Grunow) Moser et al. 1998 strain AT-70Gel18, and Sellaphora cf. minima clone BM42 ( Fig. 165 ). Other strains of Mayamaea Lange-Bertalot 1997 in the database were united in a separate clade (which was not, however, separated from the Eolimna / Sellaphora / Mayamaea clade by robust splits; nonetheless Mayamaea itself is polyphyletic in this analysis). Sellaphora Mereschowsky 1902 was not recovered as a robust clade (but would have been if Mayamaea and Eolimna were incorporated into this genus). The length of the fragment from the Styx strain was 590 bp, and the total dataset was 1473 bp long, with 270 variable sites (190 parsimony informative, 95 occurring within the fragment of the Styx strain). The model chosen and implemented in the Bayesian analysis was T92+G+I.

Observations: —The strains of Mayamaea atomus – AT-199Gel01, AT-115Gel07 and AT-101Gel04 – for which rbc L sequence information is available appear to represent two different genera. For the first of these three (designated here as E. krummensis ), which matches the Styx strain, LSU rDNA data are not available, and we suspect that this strain was omitted from the rbc L and combined analyses of Bruder & Medlin (2008) as a result. We have been unable to access descriptive or illustrative material of strain AT-199Gel01.

Strain AT-199Gel01 and the Styx strain are sister taxa corresponding to the genus Eolimna in our analyses. However, this genus also poses nomenclatural difficulties. As currently circumscribed it is polyphyletic (e.g. Beszteri et al. 2001), and because the type species of the genus is only known from the fossil record ( Schiller & Lange-Bertalot 1997), the lineage possessing nomenclatural priority is uncertain. We assume, as have others in effect (e.g. Behnke et al. 2004, Evans et al. 2008) that the branch containing E. minima corresponds to Eolimna . However, the existence of Eolimna makes a large clade of Sellaphora isolates paraphyletic ( Evans et al. 2008). Eolimna should thus be submerged into Sellaphora (or the generic name that this clade of the current Sellaphora eventually adopts). Until Sellaphora is revised as a whole, we retain the genus Eolimna for our specimens (since this name could eventually apply to all of clade 2 from Evans et al. 2008). Mayama (1999) suggested that the occurrence of two parietal plastids per single cell may be characteristic of Eolimna (vs a single H-shaped plastid in Sellaphora ; Mann 1989), and our results support this. However, we note that the H-shaped plastid in Sellaphora may sometimes fragment into two (see below) making this character potentially unreliable.

Eolimna krummensis sp. nov. can be distinguished from E. minima by the areolae which are (often much) wider near the raphe in the former species, decreasing in diameter towards the valve margins. Micrographs of cleaned valves show that Eolimna minima has a thickened central area ( Krammer & Lange-Bertalot 1986). The European and New Zealand isolates of E. krummensis are genetically distinct from E. minima ( Fig. 165 ). This, therefore, is an interesting example of “pseudocryptic species” sensu Mann & Evans (2007). To our knowledge, no other species of Eolimna exhibit the pattern of areolae reduction displayed by E. krummensis ( Moser et al. 1998; Blanco et al. 2009; Kulikovskiy et al. 2010).

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 112–129. Eolimna krummensis, strain LCR-S:10:2:1, CHR618418. Scales: Fig 112, 10 µm; Fig. 120, 5 µm (use in Figs 113–120); Fig. 121, 1 µm; Fig. 122, 1 µm (use in Figs 122–129). Fig. 112. Live cells viewed by LM, showing plastids which are typically paired and appressed to valve margins. Figs 113–120. Cleaned frustules viewed by LM, showing size variation and central thickening (girdle view in Fig. 120, showing planar valve faces). Figs 121–129. Cleaned frustules viewed by SEM. Fig. 121, frustule ends in valve and slightly oblique girdle views, showing planar valve faces and larger areolae adjacent to raphe; Figs 122–125, valves in which the size gradient of areolae is much reduced or absent (internal view in Fig. 125); Figs 126–129, valves in which the areolae adjacent to the raphe are distinctly larger than those towards the margin (internal view in Fig. 129).