Luticola darwinii, 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 : 206-207

Luticola darwinii sp. nov. Witkowski, Bąk, Kociolek, Lange-Bertalot & Seddon

Figs 51–64

Description: —Light microscopy—Valves elliptical-lanceolate with broadly rounded ends in smaller specimens and lanceolate with very weakly protracted, obtusely rounded ends in longer specimens. Valve margins appear slightly asymmetrical, being somewhat less convex on valve side with stigma. Length 15–28 μm, breadth 6–8 μm (n=20). Axial area narrow, expanded at valve centre to wide, nearly-rectangular fascia almost completely extended to valve margins, bordered by 4 to 5 areolae on either side. On one valve side punctiform stigma clearly set off from valve margin and shortened marginal stria ( Fig. 64 —arrow). Striae radiate throughout, 20–22 in 10 μm. Areolae somewhat irregularly spaced, 20–25 in 10 μm. Proximal ends of raphe branches distinctly bent to opposite side of stigma ( Fig. 63 —arrows). Distal raphe ends curving to same side.

Scanning electron microscopy:—Proximal raphe ends double curved long fissures. Distal raphe fissures long, question mark shaped, extending onto valve mantle. External areola openings bordering fascia smaller than others. Stigma approximately circular positioned in small groove.

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—7872 MCCDRS) in Coll. the Herbarium ( CDS) of the Charles Darwin Foundation at Galapagos, represented by Fig. 54 .

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: —Species dedicated to Charles Darwin.

Distribution: —Species so far found only in the type location.

Comments: —Valve outlines of specimens of L. darwinii are remarkably similar to L. falknerorum Metzeltin & Lange-Bertalot (2007: 156) . The two species differ by longer valves (up to 46 μm) of L. falknerorum and fine structure of the areolae on the valve surface. L. acidoclinata Lange-Bertalot in Lange-Bertalot & Metzeltin (1996: 76) is similar to the new species, but in L. acidoclinata striae are composed of 3–4 areolae vs. 4–5 in L. darwinii . In LM view there are also similarities with L. mitis Levkov, Metzeltin & A. Pavlov (2013: 161) . Luticola darwinii can be differentiated by the s-shaped proximal raphe endings vs. the proximal raphe ends of L. mitis which are simpler, deflected and expanded into small pores.

Figures

FIGURES 51–64: Luticola darwinii sp. nov. Figs 51–60: LM images. Valve views, showing size diminution series. Fig. 54 is of the holotype. Figs 51, 55, 57–59: with DIC, differential interference contrast, remaining bright field. Scale bar = 10 μm for LM figures. Figs 61–64: SEM external valve views. Figs 61, 62: narrow axial area expanded at the centre to form a wide rectangular fascia, extended to the valve margins, with 4–5 striae on either side. Fig. 63: radiate striae with irregularly spaced areolae. Proximal raphe ends strongly bent towards the valve primary side (arrows), distal raphe ends strongly hooked into one side. Fig. 64: note the punctiform stigma, clearly set off from the shortened marginal striae (arrow).