Cyclotella stipata, Frenguelli, 1942

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 : 121-123

Cyclotella stipata Frenguelli’s 1942 ( Figs 1–33 )

Frenguelli described this species from mosses and attached algae in small streams located in Neuquén Province, Argentinean Patagonia. The cells were described as 33–44 μm in diameter with 12 striae in 10 μm, arranged in radial rows and delimiting a rather reduced hyaline central area ornamented with a crown of ten rounded papillae, five bigger alternating with five smaller ones. Frenguelli (1942, p. 213) named the new species as Cyclotella stipata and compared it to the presumably allied Cyclotella sevilleana Deby (1884: 49) and C. sexpunctata Deby (1884 , (?) (according to) Pelletan 1889: 20 7).

The author recorded this species in two samples from Neuquén: Series 375 (as very rare) and Series 428 (as rare). SEM analysis of the only raw sample available (Series 375), yielded no specimens of this taxon leaving the ultrastructure of the type material up to now unknown. Our LM observations of the original Frenguelli material (n= 39) ( Figs 1–14 ) show round specimens, 14–69 μm in diameter, a mantle height of 22–38 μm, with 6–11 carinoportulae alternating with rimoportulae in a hyaline area at or near the center of the valve ( Figs 1–10 ). Striae on the valve face are of different lengths, (10) 12–15 (16) in 10 μm, with an areola density of (10) 13–16 (18) in 10 μm. Striae on the valve mantle are arranged in longitudinal rows, parallel to the pervalvar axis, 16 in 10 μm, with 17–18 areolae in 10 μm ( Figs 11–14 ). Frenguelli (1942) did not designate a type for this species ; he provided two micrographs of different specimens in valve view (Pl. XII figs 5 and 6) and a line drawing of a specimen in girdle view (fig. 2 in p. 213) but he did not refer them to a specific sample (either 375 or 428).

Specimens of C. stipata were also found in materials collected in Tierra del Fuego (n= 40), both in the Frenguelli Collection (Series 239) and in more recent samples (LPC 4682); they are illustrated with LM and SEM in Figs 15, 18, 20, 22 , 25–26, 28–30, 31–33 . Valves are smaller than those in Frenguelli’s original material, 17–47 μm in diameter, with 4–8 carinoportulae alternating with rimoportulae in a hyaline area at or near the center of the valve ( Figs 15, 18, 20, 22 ). Scattered spines, broadly expanded at the base, are evident at the margin of the valves ( Figs 25, 26 ). Striae of varying lengths are present, 12–16 in 10 μm having 12–16 areolae in 10 μm. Valves are elongated, with mantle heights ranging from 20.5–28 μm long. Frustules are 44.5–94 μm long. On the valve mantle stria number is 14–18 in 10 μm, with 15–20 areolae in 10 μm. A distinct, unornamented collum is evident ( Fig. 25 ).

Specimens conforming to C. stipata from the Limay River basin (n= 36) are presented in Figs 16–17, 19, 21, 23–24 and 27 (LM and SEM).Valves of this population were also smaller than the type population, 17–51 μm in diameter, having striae of varying lengths, 14–19 in 10 μm. Areolae within a stria on the valve face are 14–19 in 10 μm. 4–10 carinoportulae alternate with rimoportulae and are located in a small hyaline area in the center of the valve ( Figs 16, 17, 19, 21, 23 ). Valves are elongated about the valve mantle ; valve mantle height is 20.5–28 μm and frustules are 53–150 μm long about the pervalvar axis. Stria number on the mantle is 14–18 in 10 μm, and areola number is 15–19 in 10 μm. Small spines are evident around the margin of the valve when observed in girdle view ( Fig. 27 ).

When examined with SEM, specimens from Tierra del Fuego and Limay River exhibited similar morphologies. The valve face is slightly concave or more or less flat, with or without numerous siliceous nodules or spinules lined up externally with the striae ( Figs 18, 19 ). The transition from the valve face to the mantle is abrupt at nearly a 90-degree angle. Externally areolae appear as small, rounded pores ( Fig. 20 ). The center of the valve has distinct openings of the carinoportulae ( Fig. 20 , arrow), but openings of the rimoportulae are less evident ( Fig. 20 , arrowhead). The mantle has fine rows of small, rounded areolae ( Figs 25–27 ). Internally, areolae are unoccluded ( Fig. 28 ). In the center of the valve a thickening encircles the carinoportulae, which have unoccluded openings ( Figs 22, 23 , arrows). The rimoportulae are smaller, with narrow openings bordered by thin thickenings on either side ( Figs 22, 23 , arrowheads). A narrow rim extends internally on the valve mantle margin ( Fig. 28 ).

The cingulum may contain up to 9 open copulae. Each copula has several rows of poroids, and then a narrow or wide unornamented area. Poroids can be aligned into rows or more scattered across a copula. An elongate ligula fits into the slit or anti-ligula of the adjacent copula ( Figs 31, 33 ).

Description of new taxa of Orthoseira

Figures

FIGURES 1–14. “Cyclotella stipata Frenguelli”. LM. Specimens from the type population. 1–9. Valve views showing population variability. 10. Detail of valve face, note the hyaline area at center with the ring of carinoportulae (arrowhead) alternating with rimoportulae (arrow). 11–12. Frustule in girdle view, showing the smooth collum and the internal thickening at the mantle margin. 13. Valve in girdle view, note the copulae ligulated with distinct poroids. 14. Frustules in girdle view showing linking spines. Scale bars: Figs 1–14 = 10 μm; bar length is the same in all figures except Fig. 10.

FIGURES 15–24. “Cyclotella stipata Frenguelli” from Tierra del Fuego (Figs 15, 18, 20, 22) and Limay River basin (Figs 16–17, 19, 21, 23–24). 15–17. LM. Valve views. 18–23. SEM. 18–20. External valve views. 18–19. Whole valves, note marginal spines and spinules lined up with the striae. 20. Detail of central hyaline area showing external openings of carinoportulae (arrow) and rimoportulae (arrowhead). 21–24. Internal valve views. 21. Whole valve. 22–23. Details of valve center, note the internal openings of carinoportulae (arrow) and rimoportulae (arrowhead). 24. Detail of striae arrangement. Scale bars = 10 μm (Figs 15–18, 21), 5 μm (Figs 19, 24), 2 μm (Figs 20, 22–23).

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).