Orthoseira frenguellii Guerrero, Kociolek et Vouilloud, 2018

Guerrero, J. M., A. A. Vouilloud, Sala, S. E., Kociolek, J. P. & Vijver, B. Van De, 2018, New species and a new genus of the Orthoseirales from Patagonia, Argentina, with comments on systematic affinities within the Order, Phytotaxa 345 (2), pp. 119-132 : 126

Orthoseira frenguellii Guerrero, Kociolek et Vouilloud spec. nov. ( Figs 54–71 )

Description:—Valves rounded, showing an irregular, marginal ring of small spines ( Figs 59, 60, 63, 65 ). Valve dimensions (n=26): diameter 23.5–50.5 μm. Striae on the valve face of varying length, branching near the mantle, 10–14 in 10 μm, composed of dash-like areolae, 10–12 in 10 μm ( Fig. 60 ). Central area hyaline with 2, rarely 3 carinoportulae ( Figs 54–62 ). Small spine-like structures scattered on the valve face among the striae and onto the central area, clearly visible in LM ( Figs 55, 58, 61 ). Mantle striae parallel to the pervalvar axis, 12–15 in 10 μm, composed of distinct areolae decreasing in size to the mantle edge, 12–14 in 10 μm; interstriae on the valve mantle thickened ( Figs 67, 71 ). Internally, areolar foramina occluded by small siliceous ingrowths extending into the lumen ( Fig. 70 ). Carinoportula openings nearly round, partially occluded by a lobed silica structure ( Fig. 69 , arrow). Small slits irregularly packed between the carinoportulae ( Fig. 69 , arrowhead). Girdle with numerous copulae, each one with 1–2 rows of poroids ( Fig. 71 ).

Type:— ARGENTINA, Small creek near Copahue Volcano, Neuquén, Collector J. Frenguelli, 02/05/1932. (holotype Frenguelli Collection, Series 375, Slide 2, finder J 29, here illustrated as Figs 54–55 ).

Etymology:—named in honor of Dr. Joaquín Frenguelli for his many contributions to science in Argentina, especially with regard to his work on diatoms.

Remarks:—in a few specimens of the studied population, stria and areola densities on the valve face are beyond the range given in the description (see Table 1). This species differs in LM from O. ferrarioana in the number of carinoportulae; stria and areola densities, both on the valve face and on the mantle. In SEM further differences are evident: presence of small ingrowths in the internal areolae openings; morphology of the internal occlusion of the carinoportulae and number and arrangement of the central slits. Neither this species nor O. ferrarioana have internal valves or caverns. The structure of the slits placed between the carinoportulae is similar to that described in other species of the genus Orthoseira ( Crawford 1981, Spaulding & Kociolek 1998, Van de Vijver & Kopalová 2008) but they clearly differ in their arrangement in groups.

This species differs from other Orthoseira species in having a particular combination of characters such as valve face striae branching near the mantle; internal areola foramina with small siliceous ingrowths, carinoportula openings partially occluded by a lobed silica structure and slits irregularly packed.

Figures

FIGURES 54–71. Orthoseira frenguellii spec. nov. Specimens of type population.54–64. LM. 65–71. SEM. 54–62. Valve views showing population variability. 54–55. Holotype. 63–64.Valves in girdle view. 65–67. External valve views. 65. Whole frustule in oblique view. 66. Detail of valve center showing external openings of carinoportulae (arrow). 67. Detail of valve in girdle view; note the thickened interstriae. 68–70. Internal valve views. 68. Whole valve. 69. Detail of valve center; note the internal opening of the carinoportula (arrow) and packed slits (arrowhead). 70. Detail of areolae showing the siliceous ingrowths on the foramina.71. Valve in girdle view; note copulae with rows of poroids. Scale bars = 10 μm (Figs 54–65, 68, 71), 5 μm (Fig. 67), 2 μm (Fig. 66); 1 μm (Figs 69–70). Bar length is the same in all LM figures.