Nitzschia australodesertorum Lehmkuhl, T. Ludwig & C. Bicudo, 2019

Lehmkuhl, Elton A., Morales, Eduardo A., Tremarin, Priscila I., Bartozek, Elaine C. R., Zorzal-Almeida, Stéfano, Ludwig, Thelma A. V. & Bicudo, Carlos E. De M., 2019, Two new species of Nitzschia (Bacillariaceae, Bacillariophyta) from tropical reservoirs of southeastern Brazil, Phytotaxa 399 (1), pp. 83-99 : 89-93

Nitzschia australodesertorum Lehmkuhl, T. Ludwig & C. Bicudo sp. nov. ( Figs 32–52 , 59–68 )

LM: Frustules with nitzschioid symmetry ( Figs 41, 51, 52 ), rectangular in girdle view ( Figs 51–52 ). Valves linear-elliptic to elliptic ( Figs 32–50 ). Apices protracted, subcapitate ( Figs 37, 40–42, 47, 48, 50 ) to capitate ( Figs 32–36, 38, 39, 43–46, 49 ). Fibulae unevenly spaced, sometimes with variable shape in the same specimen, forked ( Figs 32–34, 37–40, 42, 43, 45, 47–50 ), slightly extended across the valve ( Figs 32, 34, 36–43, 47, 50 ), rounded ( Figs 36, 37, 41, 44–46, 48, 50 ), short rectangular ( Figs 32–38, 40, 43, 44, 46–49 ). Gap present between the two central fibulae, evident (arrows, figs 32, 35, 43–45, 49, 51, 52) or not evident ( Figs 33, 34, 36–42, 46–48, 50 ). Fibulae distant, every 1–3 striae. Striae parallel at the valve centre, becoming curved from one-third of the valve length until the apices. Areolae rounded, delicate, visible under LM.

Dimensions: length: 16–20 μm; width: 3–4.5 μm; 9–12 fibulae in 10 μm; 24–25 striae in 10 μm; 24–28 areolae in 10 μm (n = 50).

SEM/TEM: Internal valve face flat ( Figs 59–63 ). Marginal keel rising from the valve face ( Figs 61 , 64 ). Raphe continuous ( Fig 61 ), located at the marginal keel between the valve face and the mantle ( Figs 60, 61 , 64 ). Terminal raphe slits ending in a small helictoglossa at each pole ( Figs 59, 61 , 64, 65 ). Fibulae rounded or short rectangular ( Figs 59, 62, 63 ). Gap present in the central fibulae, evident (arrow Fig. 63 ) or not evident ( Fig 59 , 66 ). Interfibular space circular, smaller than the fibulae ( Figs 59, 62, 63 ). Striae formed by single rows of areolae ( Figs 59–63 , 66–68 ), straight at the valve centre, becoming curved from one-third of the valve length until the apices ( Figs 59, 60 , 66 ). Internal virgae flat ( Figs 59–63 ). Areolae rounded to elliptical, showing different sizes along the valve face ( Figs 59–68 ). Elongated areolae bordering the opposite raphe side ( Figs 59–67 ), occluded by hymenes ( Figs 67, 68 ). Mantle on the keel side with two areolae forming each stria; thicker virgae at mantle margin ( Figs 59–61 , 64, 65 ).

Etymology: the epithet refers to its resemblance to N. desertorum Hustedt (1949: 50) and its occurrence in the southern region.

Diagnosis: Nitzschia australodesertorum differs from N. desertorum by the presence of a gap between the central fibulae, and by the even density of fibulae throughout the whole margin. It differs from N. supralitorea by the valve outline linear-elliptic to elliptic, presence of a gap between the central fibulae, the lower density of fibulae, and the higher striae density.

Type: — BRAZIL, São Paulo State: Municipality São Paulo, Tatu reservoir, from surface sediments, 22º39′12′′S, 47º16′59′′W, 18 July 2013 (Holotype SP! 469268, depicted in Fig. 42 ).

Ecology: Nitzschia australodesertorum was recorded from seven samples of surface sediments, phytoplankton, and periphyton of Tatu reservoir, which ranged from oligo to mesotrophic conditions (see Table 3 for the abiotic characterization of Tatu reservoir). The greatest relative abundance of this species was registered from surface sediments (20.3%) and phytoplankton (3.3%). Tatu is considered a river-like reservoir due to its low residence time ( Mansor 2005), high turbidity during intense rainfalls, and the presence of banks of macrophytes along its margin.

Achnanthidium catenatum (Bily & Marvan) Lange-Bertalot (1999: 271) (18.4%) and A. minutissimum (13.2%) were the most abundant species from surface sediments, co-occurring with Nitzschia amphibia , N. australodesertorum , N. acidoclinata , N. palea , N. pusilluhasta , N. recta Hantzsch ex Rabenhorst (1862: 1283) , N. semirobusta , N. subacicularis , and N. terrestris . Other co-occurring species that were abundant in the phytoplankton during the winter were A. exiguum (Grunow) Czarnecki (1994: 157) (25.6%), A. minutissimum (17.3%) and Fragilaria sp. (17.3%). Nitzschia amphibia , N. clausii , N. palea , and N. pusilluhasta were also registered but with a low abundance (<2%).

Figures

FIGURES 32–52. Type material of Nitzschia australodesertorum sp. nov., LM. 32–50. Valve view. 51, 52. Girdle view. Arrows indicate the gap between the central fibulae. Figures marked with “=” are the same frustules with a different focus. Scale bar = 10 μm.

FIGURES 59–63. Type material of N. autralodesertorum sp. nov., SEM. 59–61. Valve face in internal view showing margin, fibulae, areolae, virgae, helictoglossae and raphe side mantle in external view. 62. Central valve face in internal view showing margin, fibulae, areolae, and raphe side mantle in external view. 63. Central valve face in internal view showing margin, fibulae, interfibular spaces and areolae. Gap between the central fibulae (arrow). Scale bars: Figs 59–61 = 5 μm; Fig 62–63 = 1 μm.

FIGURES 64–68. Type material of N. australodesertorum sp. nov. 64, 65. SEM.Apex in internal view showing helictoglossa and areolae. Mantle in external view showing keel, virgae and mantle areolae. 66–68. TEM. 66. Valve view, pattern of striae, fibulae, and elongated areolae (arrows). 67. Areolae, areola occlusion, and elongated areolae (arrows). 68. Areolae occluded by hymenes. Scale bars: Fig 64, 65 = 1 μm; Fig 66 = 5 μm; Fig 67 = 0.5 μm; Fig 68 = 200 nm.