Frustulia galapagosaxonica, 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 : 208-210

Frustulia galapagosaxonica sp. nov. Lange-Bertalot, Witkowski & Bąk

Figs 65–87

Description: —Light microscopy—Valves lanceolate with very slightly to moderately protracted, obtusely rounded ends. Length 40–77 μm, breadth 10.5–15 μm (n=30). System of median costa, consisting of raphe sternum with axial ribs at each side and helictoglossae, is straight and regularly slightly constricted (appearing concave) at central nodule. Transapical striae and areolae difficult to discern in light microscope without particular lighting effects (oblique light or interference contrast illumination).

Scanning electron microscopy:—External view ( Figs 78–83 ). Transition of valve face towards valve mantle gradual. Outer raphe slit, lying in smooth sternum (axial area) almost straight, ending proximally ( Fig. 81 —arrow) and distally ( Fig. 81 —arrowhead) in T-shaped process. Axial area expanded to rather small apical area above T-shaped processes, not opened up to valve poles ( Fig. 83 —arrow). Small open areolae arranged in 32–33 transapical striae in 10 μm and, slightly denser spaced, in about 36 apical lines in 10 μm. External opening of areolae elliptical. Transapical striae and areolae are aligned apically. Areolae parallel or subparallel, subapical areolae weakly convergent. Areolae density 32–36 in 10 μm.

Internal view ( Figs 84–87 )—helictoglossae very little produced from axial ribs. Helictoglossae porte-crayon-like, protracted ( Fig. 86 —arrow). Internal opening of areolae mostly round, elongated elliptical at valve poles.

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—7873 MCCDRS) in Coll. Herbarium ( CDS) of the Charles Darwin Foundation at Galapagos, represented by Fig. 67 .

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 name refers to type location at one of the Galápagos Islands—Isabela (Albemarle) Island and resemblance to F. saxonica from the Holarctic botanical realm.

Distribution: —This species was found so far only in five samples from the Lagoon Diablas. Besides the floating moss sample, where this species was most abundant, it has been found in samples from mangrove roots and microbial mats (see also comments below). As Conroy et al. (2009) list F. saxonica from El Junco Lake from San Cristobal Island in Galapagos, it must be checked in the future whether the El Junco species conforms to newly described F. galapagosaxonica or perhaps conforms with the South American species “ F. aff. saxonica ” (cf. Rumrich et al. 2000).

Comments: —The complex of fine external valve structures in F. galapagosaxonica conforms in general to the pattern shown for F. saxonica Rabenhorst (1853: 50) , the type species of this genus (see Lange-Bertalot 2001, p. 161, 172). However, the orientation of the transapical striae are more strongly convergent towards the apices in F. saxonica . Density of apical lines is lower in F. saxonica , 28–31 vs. about 36 in 10 μm in F. galapagosaxonica . The most closely resembling specimens from South America are recorded as “ Frustulia aff. saxonica ” in Rumrich et al. (2000, figs 96: 5,6) originating from the Lake District of southern Chile, one collected from a lake, the second one from a creek near a volcano. However, the density of transapical striae and apical lines is lower (both specimens with about 27–28 in 10 μm), while the orientation of the striae conforms to the new taxon.

Figures

FIGURES 65–77: Frustulia galapagosaxonica sp. nov.LM images.Valve view, showing size diminution series.Fig. 67 is of the holotype. Figs 72–77: with DIC, differential interference contrast, remaining bright field. Scale bar = 10 μm.

FIGURES 78–83: Frustulia galapagosaxonica sp. nov. SEM external valve views. Figs 78, 79: axial area of the whole valve, with straight outer raphe slit. Figs 80–82: T-shaped proximal (Fig. 81–arrow) and distal (Fig. 81–arrowhead) raphe ends. Fig. 83: Transapical striae composed of apically aligned areolae. Note small terminal nodule area above the T-shaped distal raphe end (arrow) terminating below the pole.

FIGURES 84–87: Frustulia galapagosaxonica sp. nov.SEM internal valve views. Fig.84: the entire valve with axial ribs runing alongside the raphe slits. Note the presence of the double helictoglossa at the central nodule. Figs 85–87: apical parts of valves with porta-crayon-like protracted helictoglossae (arrow in Fig. 86).