Luticola galapagoensis, 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 : 203-205

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

Figs 2–50

Description: —Light microscopy—Valves elliptical-lanceolate to elliptical, with broadly rounded and not protracted apices. Length 8–27 μm, breadth 5–8 μm (n=30). Axial area narrow, straight, expanded at valve centre to wide, rectangular fascia extended to valve margin ( Figs 34–39 ). At valve margin fascia bordered by 3–4 areolae on either side, on one side an additional opening represents stigma foramen which is elongated transapically. Raphe filiform, straight, with external proximal ends distinctly deflected in same direction (away from stigma, Fig. 37 —arrows) and external distal ends deflected in same direction as proximal ends, curved like a question mark onto valve mantle. Striae number 18–24 / 10 μm.

Scanning electron microscopy:—Internal distal raphe ends terminate as small helictoglossae. Striae radiate, strongly so towards the apices, distinctly punctate, with each stria comprised of 3–6 rectangular or dash-like areolae. Areolae density 20–24 in 10 μm. Single areola per stria is evident on valve mantle ( Figs 34, 37 , 40 —arrow). Internally, striae occluded by hymenes that run across all areolae, not localized to each opening ( Fig. 42 —arrow and Fig. 46 — arrowhead). Stigma foramen slightly differentiated from areolae and extends internally at an acute angle (see SEM views Figs 39 , 41 —arrows). Internally the stigma is positioned about half the way between the centre and the margin, the opening is indistinct, and bordered by a hemispherical lipped structure (see SEM views Figs 44, 45, 48, 49 —arrows). Internal proximal raphe ends straight, simple, and just terminating on the stauros. Longitudinal canal is evident near valve margin, distinct, protruding into valve interior and occluded by hymens ( Figs 43 , 46, 47, 50 —arrows).

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—7871 MCCDRS) in Coll. Herbarium ( CDS) of the Charles Darwin Foundation at Galapagos, represented by Fig. 27 .

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 the type location at one of the Galápagos Islands—Isabela (Albemarle) Island.

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

Comments: —By far the most morphologically similar species is Luticola permuticoides Metzeltin & Lange-Bertalot (2007: 158) , originating from tropical Brazil. The two taxa differ in terms of areola density with 16–19 in 10 μm for specimens from the type population of L. permuticoides from the Itatiaia mountains, Brazil, vs. 20–24 in 10 μm in the new taxon and in terms of position and shape of stigma. In L. galapagoensis the stigma is located close to the junction between valve face and mantle and in LM visible as elongated slit, vs. somewhat distant from the junction and less elongated in L. permuticoides .

Figures

FIGURES 2–33: Luticola galapagoensis sp. nov. LM images. Valve views, showing variation in size and outline. Fig. 27 is of the holotype. Figs 2–20: with DIC, differential interference contrast, remaining bright field. Scale bar = 10 μm.

FIGURES 34–39: Luticola galapagoensis sp. nov. SEM images. External valve views. Note the presence of narrow, straight axial area, expanded at the centre to form a wide, rectangular fascia extended out to nearly the margin, with 3–4 areolae on either side at the margin, and on one side with additional opening of stigma foramen (arrow in Fig. 39). Striae comprised of 3–6 rectangular or dash-like areolae. Note the external central raphe endings bent towards valve primary side (arrows in Fig. 37).

FIGURES 40–43: Luticola galapagoensis sp. nov. SEM images. External valve views. Fig. 40: a single areola per stria positioned along the valve mantle (arrow). Fig. 41: elongated stigma foramen, different from the striae forming areolae (arrow). Figs 42, 43: FIB cut of the frustule, Fig. 42: position of the hymenate areola occlusions (arrow). Fig. 43: note the longitudinal canal (arrow).

FIGURES 44–50: Luticola galapagoensis sp. nov. SEM images. Internal valve views. Figs 44, 45, 48, 49 (arrows): note the opening of stigma bordered by a hemispherical lipped structure. Fig. 46: close up of the valve interior showing the hymenate occlusions of areolae (arrowhead). Figs 46, 47, 50: note the longitudinal canal near the margin of valve, protruding into the valve interior. Arrow in Fig. 50 points to an opening of the canal. Figs 49, 50: FIB cut of the valve.