Luticola coloradiana, Shea, Greifenstein & Kociolek, 2022

Shea, Rachel, Greifenstein, Jeremy & Kociolek, J. P., 2022, Valve Ultrastructure and Description of a new Luticola D. G. Mann (Bacillariophyceae) species from Colorado, USA, Phytotaxa 554 (3), pp. 269-277 : 270-273

Luticola coloradiana, Shea, Greifenstein & Kociolek , sp. nov. ( Figs 1–19 )

Description: In LM ( Figs 1–8 ) valves are rhombic-lanceolate to rhombic in smaller specimens. Valves measure 23.0– 70.0 µm in length, 11.0–18.5 µm in breadth. Raphe branches are axial, along the apical axis. Isolated stigma near center of valve. Striae radiate outwards, non-uniform in appearance, often becoming smaller close to valve margin, 10–12 in 10 µm.

In the SEM, the valve exterior has a rugose appearance, formed by thickened ridges running longitudinally along the apical axis of the valve and by areolae being located in depressions on the valve face ( Figs 9–11 ). Areola density 11–14 / 10 µm. There is an elevated ridge running around the entire margin of the valve ( Fig. 11 ). The axial area is straight, expanded slightly towards the central area, rectangular in shape and without areolae, only a single, small stigma opening ( Figs 9–13 ). The stigma opening is smaller than the areolae. The central area may also bear numerous small depressions that do not penetrate the valve ( Fig. 13 ). The areolar depressions and the smaller, more shallow ones around the central area may have small granules in and around them. The raphe is straight, with proximal ends bent to one side (opposite the stigma) and distal ends bent in the same direction, opposite the direction of the proximal ends. The raphe slit is bordered by a thin rim of silica ( Figs 9–11 , 12, 14 ). The mantle of the valve has a row of small poroids and a row of prominent, elongated poroids ( Fig. 15 ). Girdle bands number 4–5 / valve and have a single row of poroids situated towards the valve.

The valve interior has an expanded axial area that is developed into a central area formed by a stauros that extends nearly to the margin ( Figs 16, 17 ). Areolae do not appear occluded internally ( Fig. 16 ). Proximal raphe ends terminate at the base of the central area ( Figs 16–18 ) while the distal ends terminate in small helictoglossae ( Fig. 19 ). On one side of the central area is the stigma opening. The stigma opening is simple, round, with a short, thickened collar ( Figs 16–18 ). Areolae are round to dash-like in shape. The valve interior, like the exterior, appears rugose ( Figs 16, 17 ). Thick siliceous ribs extend from the margin, and on the valve face there is a line of thin, fimbriate siliceous structures that are aligned with the ribs ( Figs 16, 17 ).

Type: — USA. Colorado, Gunnison County. Unnamed wet meadow in Gunnison County, Colorado, USA. Latitude : 38.25025126, Longitude : -107.497408. Collection was made on August 2, 2021. Holotype Slide: JPK Collection ( COLO!) 651052 Isotypes: To be deposited at Academy of Natural Sciences (Philadelphia) and the Natural History Museum (London).

Etymology: —Named for the state of Colorado in which it occurs.

Ecology: —While no other data on the physical and chemical characteristics of the collecting site were obtained, the associated diatom flora is diverse, with unnamed species of Aulacoseira Thwaites and Encyonopsis Krammer , as well as Cavinula davisiae Bahls (2013: 15) and several species of cymbelloid diatoms being present.

Figures

FIGURES 1–8. Luticola coloradiana, sp. nov.Light microscopy.Valve views. Size diminution series.All specimens are from the holotype slide. Scale bar = 10 µm for all images.

FIGURES 9–11. Luticola coloradiana, sp. nov. Scanning electron microscopy. External valve views. Figures 9–11. Valves demonstrate rugose nature of the valve face. Striae appear interrupted longitudinally. Proximal raphe ends are deflected towards the same side; stigma opening is positioned on the opposite side. In figures 10 and 11, the margin of the valves has an elevated ridge. In figure 11 the mantle of the valve has a series of elongated areolae. Scale bars = 5 µm.

FIGURES 12–15. Luticola coloradiana, sp. nov. Scanning electron microscopy. External views. Fig. 12. Central area with deflected external proximal raphe ends.Arrow indicates stigma opening. Scale bar = 1.5 µm. Fig. 13. Showing many depressions in the central area, many of which also have very small, rounded granules. Scale bar = 1.5 µm. Fig. 14. External distal raphe end is hooked and extends onto the mantle. Scale bar = 1.0 µm. Fig. 15. Girdle view of the end of the valve. Elevated ridge around the margin of the valve is evident. There is a row of elongated areolae which have a row of smaller areolae positioned towards the valve. Cingulum elements have a row of poroids. Scale bar = 2.5 µm.

FIGURES 16–19. Luticola coloradiana, sp. nov. Scanning electron microscopy. Internal views. Figs 16, 17. Valve views, showing expanded, internally-raise fascia of the central area bearing straight proximal raphe ends, a simple stigma opening, and inwardly protruding siliceous structures from the margin and valve face. Scale bars = 10 µm. Fig. 18. Central nodule with proximal raphe ends and round stigma opening. Scale bar = 0.3 µm. Fig. 19. Distal raphe end with small helictoglossa. Scale bar = 0.3 µm.