Eunotia spatulata Veselá et Johansen, 2014

Veselá, Jana & Johansen, Jeffrey R., 2014, Three new Eunotia (Bacillariophyta) species from Acadia National Park, Maine, USA, Phytotaxa 175 (4), pp. 181-200 : 194

Eunotia spatulata Veselá et Johansen spec. nov. ( Figs 104–133 )

Type:— USA. Maine: Acadia National Park, Halfmoon Pond, 44.391172° N, 68.251052° W, 10 June 2008, Veselá 081b ( ANSP!). Water characteristics: pH 4.6, water temperature 24.6°C, conductivity 22.9 µS. The holotype designated here, holotype slide ANSP GC 59086, Fig. 114 depicts the holotype (118.85 mm south by 122.2 mm east from the benchmark cross on the slide); isotype slide ACAD 54652b, stored at J. R. Johansen’s collection at John Carroll University, Ohio , USA (isotype specimen in Fig. 116 , 8.9 mm south by 8.4 mm west from the benchmark cross on the slide).

Valves are straight, narrowing very gradually and slightly from the center to the subapical portion, from which the valves widen abruptly into the widely spatulate apices ( Figs 104–117 ), 159–272 µm long, 3.3–4.0 µm wide in center, 1.9–2.8 µm wide in narrowest part, 5.3–6.4 µm wide at apices. The apices are inflated more on the dorsal side than the ventral side and appear flattened at the ends ( Figs 104–117 ). The valve edges are sharply beveled with one to two rows or areolae in the beveled section ( Figs 120, 121, 124 ). Irregularly arranged siliceous ridges are present at the apical margins of the valves ( Figs 119, 121–123 ). Raphe begins on the valve mantle, and curves subapically on the valve face back towards the main part of the valve. It is centered with respect to the main axis of the valve but closer to the ventral margin because of the unevenly widened apices ( Figs 119, 121–123 ). External raphe fissure is visible on the external portion of the valve (e.g., Fig. 122 ), but does not penetrate the internal part of valve past the helictoglossa, where it is internally occluded by a hyaline linear area interrupting the striae past the helictoglossa ( Figs 126, 127, 130, 131 ). A single rimoportula is present on each valve, and is located within the apical edge adjacent to the helictoglossa ( Figs 122, 123 , 127, 129 ), usually visible in the LM ( Figs 104b, 105b, 107b ). Striae are fine and parallel throughout the valve, including the apices, where they are spaced more densely ( Figs 126–133 ), 18–21 in 10 µm, up to 23.5 in 10 µm at the ends. Areolae are circular and externally occluded ( Fig. 122 ), 33–40 in 10 µm.

Etymology:—From the Latin spatulata , referring to the spatulate outline of the valve apices.

Ecology and distribution:— Eunotia spatulata was observed in only six localities (mostly ponds) from Mount Desert Island, Acadia National Park, Maine, USA ( Table 1).

Observations:— Eunotia spatulata is similar to Eunotia eurycephala (Grunow in VanHeurck 1881: fig. 35:8) Nörpel-Schempp et Lange-Bertalot in Lange-Bertalot & Metzeltin (1996: 48), from which it differs by having longer valves and more broadly widened apices ( Table 2). It is also similar to Eunotia eurycephaloides Nörpel-Schempp et Lange-Bertalot in Lange-Bertalot & Metzeltin (1996: 48), from which it differs by having straight, non-arcuate valves and much more broadly widened ends ( Table 2).

E. spatulata is part of a species cluster that includes E. eurycephala and E. eurycephaloides . Grunow showed only one drawing of what he called “ E. flexuosa var.? eurycephala ”, and it was a long, thin straight valve with distinctly widened ends (in Van Heurck 1881). Cleve-Euler gave two drawings of her interpretation of E. flexuosa γ eurycephala Grunow : one is straight while the other is very arcuate (Cleve-Euler 1953, figs 419 f, g, respectively). Apices of these valves were much larger than what other authors have shown for their taxa. Eunotia eurycephala was erected as a status novus in the same work where E. eurycephaloides was described ( Lange-Bertalot & Metzeltin 1996). Eunotia eurycephaloides was illustrated as being slightly to distinctly arcuate and 60–150 µm long, with apices not as enlarged as shown in the previous literature for E. eurycephala . Later, Lange-Bertalot et al. (2011) synonymized E. eurycephaloides with E. eurycephala stating that with more populations seen the two taxa could not be separated. We are not convinced that this is so. From the images and drawings shown for these taxa, E. eurycephaloides is arcuate and has the least enlarged apices (up to 4 µm wide), E. eurycephala is almost straight and has broader ends (up to 4.5 µm wide). Regardless of the fate of these two taxa, E. spatulata is distinct from both, with completely non-overlapping valve length (159–272 µm long compared to less than 150 µm long, Table 2), much wider non-overlapping width of the apices (5.3–6.4 µm wide, Table 2), and ultrastructural details (e.g., no irregular siliceous ridges on external apical margins of E. eurycephala ). Additionally, in none of the earlier drawings or images is the valve outline shown to distinctly narrow from the center towards the apices with the narrowest width in a subapical region of the valve. More study of E. eurycephala , E. eurycephaloides , and the related taxon E. eurycephala var. pachycephala Grunow in Van Heurck (1881: fig. 35:7) is needed to test the differences in these taxa that we can detect now with the limited study they have received.

Figures

FIGURES 104–117. Eunotia spatulata sp. nov., LM. Figs 104b, 105b, 107b Details of apices with rimoportulae and helictoglossae in focus. Fig. 112 Together with Eunotia novaeangliae. Fig. 114 Photograph of the holotype specimen (H). Fig. 116 Micrograph of the isotype specimen (Is). Pairs of photographs representing the same specimen in different focal planes or two various parts of the same valve are marked with “=”. Scale bar = 10 µm.

FIGURES 118–124. Eunotia spatulata sp. nov., external views, SEM. Figs 118–120, 121–122, 123–124 each represent parts of the same specimen. Fig. 118 Incomplete valve, although still showing the straight long valve, narrowing very gradually and slightly from the center to the subapical portion, with a widely spatulate apex. Fig. 119 Apex without rimoportula. Figs 120, 124 Details of middle parts of the valves with sharply beveled edges. Figs 121–123 Apices with rimoportula apertures and well-developed siliceous ridges at the apical valve margins. Fig. 122 Detail of externally occluded rounded areolae. Scale bars = 10 µm (in Fig. 118) or 1 µm (in Figs 119–124).

FIGURES 125–133. Eunotia spatulata sp. nov., internal views, SEM. Figs 125–128, 130 and 132, 131 and 133 each represent parts of the same specimen. Figs. 125 Complete valve. Figs 126, 130, 131 Details of apices without rimoportulae, showing more densely spaced striae and the internally occluded raphe extending past the helictoglossa. Figs 127, 129 Apices with prominent rimoportulae adjacent to helictoglossae. Fig. 128 Detail of the central part of the valve, with internally unoccluded round areolae and parallel striae. Figs 132, 133 Partial valves including the widened central portion of the valve and subapical attenuation. Scale bars = 10 µm (in Figs 125, 132, 133) or 1 µm (in Figs 126–131).

FIGURES 1–39. Size reduction series of Eunotia novaeangliae sp. nov., LM. Figs 1–34 Valve views. Fig. 6 Photograph of the isotype specimen (Is). Fig. 10 Photograph of the holotype specimen (H). Figs 35–39 Frustules in girdle views, with noticeably long raphe slits. Pairs of photographs representing the same specimen in different focal planes are marked with “=”. Scale bar = 10 µm.