Urosolenia obesa Freire, Tremarin & Ludwig 2013, sp. nov.

Urosolenia obesa Freire, Tremarin & Ludwig sp. nov.

Figs 2–27

Frustules solitary, sub-cylindrical, straight to slightly curved, 27.6–47.6 µm long (total), 6.8–14.2 µm width (n=50). Valve face conical ornamented with rounded to irregular areolae, 8–10 in 10 µm, randomly arranged and extending onto the calyptra base. Valve mantle edge surrounded by a thin hyaline margin. Calyptra straight and eccentric, 9.7–12.3 µm long, positioned at right to strongly oblique angle with the pervalvar axis. Calyptra in variable position to the frustules, it may be on the same or opposite side in relation to the pervalvar axis. Calyptra ornamented by irregular rib-like structures that extend from base until the median portion of this valve projection. Tip of spine-like extension with two small teeth and a central ligula. Terminal seta not observed. Cingulum with several semi-circular open and narrow bands, 13–16 in 10 µm, perforated by round poroids, ca. 10–11 in 1 µm. Coarser rounded pores, varying in size and number, present on both sides of the cingulum. Resting spore sub-cylindrical, with convex/concave wall, smooth, 6.2–6.5 µm long and 10.1–13.5 µm wide.

Holotype: UPCB collection No. 68864 (Universidade Federal do Paraná, Department of Botany, Brazil). Holotype illustrated in Fig. 5.

Isotype: ANSP GC 26813 (Academy of Natural Sciences, Philadelphia).

Type locality: BRAZIL. Paraná: Candói, Fundão hydroelectric reservoir, 19 March 2009, LACTEC technical equip.

Etymology: from the latin obesus, stout, plump. This refers to the wide frustules that distinguish this species from its congeners.

Additional examined samples: Capivari reservoir UPCB 59525, 60509, 68843, 68867; Guaricana reservoir UPCB 59533, 60517, 68851, 68875; São Jorge reservoir UPCB 59523, 60526, 68860, 68884; Pitangui reservoir UPCB 59537, 60521, 68855, 68879; Salto do Vau reservoir UPCB 59541, 60525, 68859, 68883; Fundão reservoir UPCB 68864, 68888; Foz do Areia reservoir UPCB 59530, 59531, 59532, 60514, 60515, 60516, 68848, 68849, 68850, 68872, 68873, 68874; Santa Clara reservoir UPCB 68863, 68887; Jordão reservoir UPCB 59520, 60518, 68852, 68876; Segredo reservoir UPCB 59543, 59544, 60527, 60528, 68861, 68862, 68885, 68886; Salto Caxias reservoir UPCB 59539, 59540, 60523, 60524, 68857, 68858, 68881, 68882; Mourão reservoir UPCB 59536, 60520, 68854, 68878.

Ecological data: Urosolenia obesa was found in reservoirs with different trophic status. Higher densities were registered in the Jordão reservoir in January 2007 (514 cells mL -1), Pitangui reservoir in April 2010 (626 cells mL -1) and São Jorge reservoir in October 2009 and April 2010 (583 and 1716 cells mL -1, respectively). In these periods, the species occurred in waters with temperature range of 19.3 to 28.8ºC, the pH varied between 7.4–7.6, total phosphorus varied from 0.02 to 0.07 µg.L -1 and total nitrogen from 0.5 to 2.0 µg.L -1. Resting spores were found in the autumn (April) during periods of higher cellular densities in São Jorge and Pitangui reservoirs.