Eunotia isabelensis, 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 : 213-214

Eunotia isabelensis sp. nov. Lange-Bertalot, Bąk & Kociolek

Figs 107–120

Description: —Light microscopy—Frustules in girdle view rectangular of variable breadth, 5–11 μm. Valves dorsiventral, ventral margin moderately concave, dorsal margin more strongly convex-triundulate with very shallow wave troughs and crests. Middle crest more prominent than other two. Ends slightly deflected dorsally but almost straight, simple, broadly rounded. Length 13–27 μm, breadth 4.5–5.0 μm (n=20). Raphe nodule close to valve pole with terminal fissures running closely parallel to valve pole, but barely visible in LM. Striae appear coarse, equidistant, 14–15/10 μm, except at valve ends where they become moderately more densely spaced, up to 20/10 μm. Areolae not discernible with light microscopy.

Scanning electron microscopy:—Dorsal and ventral external view ( Figs 118–119 ). Ventral side exhibits short raphe branches ( Fig. 118 —arrows). Unperforated area separates wider spaced virgae at the valve face/mantle junction from more narrowly spaced ones at distal edges, between mantle and valvocopula. Virgae become conspicuously shallower towards valve ends ( Fig. 118 ). Dorsal side of frustule appears far less differentiated with wavy outline weakly recognisable ( Fig. 119 ). External opening of areolae simple, round. Each stria positioned in a shallow groove. Internal opening of areolae transversely elliptic, becoming round towards valve apices, ca. 40 in 10 μm. Each stria internally positioned in a shallow ditch. Distal raphe end terminates into well-developed helictoglossa ( Fig. 120 —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—7875 MCCDRS) in Coll. Herbarium ( CDS) of the Charles Darwin Foundation at Galapagos, represented by Fig. 107 .

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

Etymology: —The name refers to location at one of the Galápagos Islands —Isabela Island.

Distribution: —As yet only known from the type location.

Comments: —No morphologically similar taxon is known from South America, from the Holarctic encompassing North America and Eurasia, or from the sub-Antarctic islands (see e.g. Lange-Bertalot et al. 1996, Rumrich et al. 2000, Lange-Bertalot et al. 2011 and Van de Vijver et al. 2014).

Figures

FIGURES 107–120: Eunotia isabelensis sp. nov. LM images. Figs 107–115: valve views, size diminution series, Figs 116, 117: frustules in girdle view. Fig. 107 is of the holotype. Scale bar = 10 μm for LM figures. Figs 118, 119: SEM girdle views of frustule. Fig. 118: ventral side of a frustule with the short raphe branches (arrows). Fig. 119: dorsal side of a frustule with less differentiated ribs and perforations than ventral side. Fig. 120: internal valve view with distal raphe end forming a well-developed helictoglossa (arrow).