New species and a new genus of the Orthoseirales from Patagonia, Argentina, with comments on systematic affinities within the Order Author Guerrero, J. M. División Ficología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s / n. 1900, La Plata, Argentina guerrero@fcnym.unlp.edu.ar Author A. A. Vouilloud División Ficología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s / n. 1900, La Plata, Argentina Author Sala, S. E. División Ficología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s / n. 1900, La Plata, Argentina Author Kociolek, J. P. Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309 USA Author Vijver, B. Van De Botanic Garden Meise, Department of Bryophyta andThallophyta, Nieuwelaan 38, B- 1860, Belgium & Department of Biology-ECOBE, University of Antwerp, Universiteitsplein 1, B- 2610 Wilrijik, Belgium text Phytotaxa 2018 2018-03-23 345 2 119 132 http://dx.doi.org/10.11646/phytotaxa.345.2.3 journal article 10.11646/phytotaxa.345.2.3 1179-3163 13705161 Orthoseira ferrarioana Guerrero, Kociolek et Sala spec. nov. ( Figs 34–53 ) Description :—Cells cylindrical joined in short chains. Valve dimensions (n=27): Frustules in girdle view 38–69 μm long. Diameter 18–31 μm. Mantle height 4.5–25 μm. Central area forming a hyaline zone with a ring of 3–4, rarely 2 carinoportulae ( Figs 34–43 ). Carinoportula openings externally surrounded by incomplete collar-like structures ( Figs 47, 48) and internally occluded by triradiate to T-shaped silica ridges ( Fig. 51 , arrow). Small slits, more or less parallel arranged between the carinoportulae ( Fig. 51 , arrowhead). Small spines present at the valve face/mantle junction ( Fig. 49 ). Areolae on the valve face 18–24 in 10 μm, arranged in radiating irregular rows, 16–20 in 10 μm lined up with siliceous nodules or spinules ( Figs 47, 48 ); areolae internally unoccluded ( Figs 52, 53 ). Mantle with parallel striae, 17–20 in 10 μm, composed of distinct areolae, 17–20 in 10 μm; margin with unornamented collum ( Fig. 49 ). FIGURES 25–33 . “ Cyclotella stipata Frenguelli ” from Tierra del Fuego (Figs 25–26, 28–33) and Limay River basin (Fig. 27). 25–29, 31–33. SEM. 30. LM. 25–27. Mantle external views. 25. Whole valve, note parallel rows of areolae and the smooth collum. 26. Detail of the valve face/mantle junction with spines. 27. Detail of spines linking two neighbor valves. 28. Broken valve in internal view, note the internal thickening at the valve margin. 29–30. Whole frustules. 31. Valve with two copulae, note the conspicuous ligula. 32. Open valvocopula ornamented with rows of poroids. 33. Open copula showing ligula and antiligula. Scale bars = 10 μm (Figs 25, 29–33), 5 μm (Figs 26–27). FIGURES 34–53 . Orthoseira ferrarioana spec. nov. Specimens of type population. 34–46. LM. 47–53. SEM. 34–43. Valve views showing population variability. 40. Holotype. 44–46. Specimen in girdle view at different foci. 47–49. External valve views. 47. Whole valve. 48. Detail of valve center showing external openings of carinoportulae (arrow). 49. Detail of valve in oblique view, note the marginal spines. 50–53. Internal valve views. 50. Whole valve. 51. Detail of valve center showing the internal openings of carinoportulae (arrow) and the slits between them (arrowheads). 52. Detail of the striae arrangement. 53. Detail of a broken valve showing the thickened interstriae. Scale bars = 10 μm (Figs. 34–47, 50), 5 μm (Fig. 49), 2 μm (Figs 48, 52–53), 1 μm (Fig. 51). Bar length is the same in all LM figures. Type: — ARGENTINA , Small creek near Copahue Volcano, Neuquén , Collector J. Frenguelli 02/05/1932 . ( holotype Frenguelli Collection, Series 375, slide 6, finder Q 29- R 29, here illustrated as Fig. 40 ). Etymology :—named in honor of our friend and colleague, Dr. Martha E. Ferrario, Museo de La Plata, for her contributions to the study of diatoms in general, and those in Argentina in particular. Remarks :—In a few specimens of the studied population, the stria and areolae densities both at valve face and mantle are beyond the range given in the description (see Table 1). This species differs from other Orthoseira species in having a particular combination of characters such as valve face striae of different length; areola internally unoccluded; the ornamentation of the external carinoportula openings, the morphologies of the internal occlusion of the carinoportulae and the arrangement of the central slits.