Pinnularia valdecontroversa, Bąk & Kociolek & Lange-Bertalot & Łopato & Witkowski & Zgłobicka & Seddon, 2017

Bąk, Małgorzata, Kociolek, John P., Lange-Bertalot, Horst, Łopato, Daria, Witkowski, Andrzej, Zgłobicka, Izabela & Seddon, Alistair W. R., 2017, Novel diatom species (Bacillariophyta) from the freshwater discharge site of Laguna Diablas (Island Isabela = Albemarle) from the Galapagos, Phytotaxa 311 (3), pp. 201-224 : 216-217

Pinnularia valdecontroversa sp. nov. Lange-Bertalot, Witkowski & Bąk

Figs 157–179

Description: —Light microscopy—Valves linear, smallest becoming weakly lanceolate. Ends variable, not protracted at all to broadly and shortly protracted with more or less bluntly rounded poles. Length 40–56 μm, breadth 7–10 μm (n=20). External raphe fissures slightly wavy ( Fig. 168 —arrow) and lateral to the internal fissures. Axial area narrow, linear. Central area forming broad fascia. Striae 8–9 in 10 μm, radiate in proximal part of valve, rather strongly pronounced in broader specimens. Striae in distal part of valve becoming strongly convergent, but not different in density.

Scanning electron microscopy:—External view ( Figs 168-173 ). Longitudinal bands marking the border between open and closed parts of alveoli absent. Valves asymmetrical about transapical axis because of terminal raphe fissures and length and density of distal, convergent striae. Proximal ends of raphe weakly expanded ( Fig. 168 —arrowhead), neither conspicuously deflected to one side. Terminal fissures indistinctly curved and sickle-shaped ( Fig. 169 —arrow), curve to opposite sides at both poles onto valve mantle ( Figs 169, 170 —arrows). Subdistal striae—each one consisting of quadri- to pentaseriate areolae—become gradually shorter at one side, and become circumradiate around valve poles. On opposite side, areolae become longer and remarkably more wavy, and finally broader near axial area. Open alveola covered with porous membranes ( Fig. 173 , 176 —arrows). Discontinuity evident between subdistal and circumpolar striae forming gap ( Fig. 171 —arrow). External raphe slit gently undulate, becoming moderately wider towards unilaterally deflected central pores. Internally, raphe fissure with intermissio at central nodule, with proximal raphe ends small, slit-shaped, bent in same direction ( Fig. 175 —arrows). Internally distal raphe ends terminate with small helictoglossae ( Fig. 179 —arrow).

Type: — ECUADOR. Galápagos Islands: Isabela (Albemarle) Island, Diablas wetlands, 0.95731°S, 90.98685°W, 23 July 2012, holotype (designated here):—Slide no. 20779 (species code—7877 MCCDRS) in Coll. Herbarium ( CDS) of the Charles Darwin Foundation at Galapagos, represented by Fig. 160 .

Type locality: —Floating moss, at the mouth of the stream to the lagoon in the Diablas wetlands—a permanent, brackish coastal lagoon network located at sea level on the south side of Isabela Island.

Etymology: —The composite epithet in Latin means very (“valde”) and controversial (“controversus”) referring to the different structured poles of every valve.

Distribution: —As yet not observed from other regions than the type location.

Comments: —Very few Pinnularia species are characterised by asymmetry of both poles. These are Pinnularia controversa Hustedt in A. Schmidt Atlas (1934) figs 385: 16–17 from Sumatra, Indonesia. The second one is P. platycephala ( Ehrenberg 1854) P.T. Cleve (1891: 20) . Details about the distinctive characters between the three Pinnularia taxa are given in the discussion.

Figures

FIGURES 157–167: Pinnularia valdecontroversa sp. nov. LM images. Figs 157–163, 165–167: valve views, size diminution series, Fig. 164: frustule in girdle view. Fig. 160 is of the holotype. Scale bar = 10 μm.

FIGURES 168–173: Pinnularia valdecontroversa sp. nov. SEM external views. Fig. 168: raphe fissure slightly wavy (arrow), proximal ends weakly expanded (arrowhead). Figs 169, 171-173: terminal raphe fissure indistinctly curved and sickle-shaped (arrow in Fig.169). Fig. 170: frustule in girdle view. Note the terminal raphe end (arrow). Fig. 171: discontinuity between subdistal and circumpolar striae resulting in a gap (arrow). Note the presence in external view of the open alveola covered with porous membranes (arrow in Fig.173).

FIGURES 174–179: Pinnularia valdecontroversa sp. nov. SEM internal valve views. Figs 174, 177: striae radiate in the proximal part of valve, in the distal part becoming strongly asymmetrical about the apical axis. Fig. 175: proximal raphe ends small, slit-shaped, bent in the same direction towards valve secondary side (arrows). Figs 176, 178, 179: distal raphe ends terminate in small helictoglossae (arrow in Fig. 179). Note the open alveolae (Fig. 176 arrow).