Nitzschia pusilluhasta Lehmkuhl & 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 : 86-89

Nitzschia pusilluhasta Lehmkuhl & C. Bicudo , sp. nov. ( Figs 2–21 , 53–58 )

LM: Frustules with nitzschioid symmetry ( Figs 8, 9, 15, 16, 18–21 ), rectangular in girdle view ( Figs 18–21 ). Valves lanceolate with slightly to clearly protracted ends ( Figs 2–17 ). Apices cuneate to rounded, sometimes somewhat asymmetrical ( Figs 2–5, 11, 12, 15–17 ) or symmetrical ( Figs 6–10, 13, 14 ). Fibulae unevenly spaced, distributed along the raphe margin; gap between central fibulae absent. Fibulae shape may vary from short rectangular ( Figs 4, 6, 7, 9–11, 13, 16 ) to slightly extended toward the valve along the virgae ( Figs 2–7, 9, 10, 12, 14, 16 ) in the same specimen. Discrete fibulae branches may be present into two or three virgae ( Figs 2–10, 12, 13 ). Fibulae distant, every 1–3 striae. Striae parallel at valve centre, becoming slightly curved and/or divergent toward the apices ( Figs 2–17 ). Areolae coarse, round to elliptic, easily discernible.

Dimensions: length: 13–29 μm; width: 3.5–6 μm; 7–12 fibulae in 10 μm; 17–19 striae in 10 μm; 10–18 areolae in 10 μm (n = 50).

SEM: Keel marginal, rounded, slightly elevated from the valve face level ( Figs 53–58 ). Raphe marginal ( Figs 54–56, 58 ), continuous from one apex to the other ( Figs 53–56 ). Terminal raphe ends curved, crossing down the apices near the mantle, drop-shaped ( Fig. 58 ). Striae formed by single rows of areolae, straight at the centre, becoming slightly curved next to the ends ( Figs 53–54 ). Areolae shape rounded to elliptical, with different sizes along the valve face ( Figs 53–58 ). Areolae next to the raphe may be single, double or triple and partially joined, and are a little further from other areolae ( Figs 53–55, 57, 58 ). On the raphe side of the mantle, there is a stria formed by two or three rounded areolae; the first areolae of each stria made of two minor areolae, or of one areola of regular size ( Figs 54, 55, 58 ). Larger and rounded areolae in line with the valve face striae, on the opposite margin to the raphe ( Fig. 57 ). Valvocopula with a row of tiny pores near the mantle; pores density 30 in 10 μm ( Figs 53, 55, 57, 58 ).

Etymology: the epithet refers to the small size and lanceolate shape of the valves.

Diagnosis: Nitzschia pusilluhasta differs from N. amphibia Grunow (1862: 574) by the absence of a gap between the central fibulae, and the outline of the valve, which is lanceolate with slightly to clearly protracted ends. It differs from N. semirobusta Lange-Bertalot (1993: 149) by the fibulae shape that is rectangular, short to slightly extended, and might be discretely branched.

Type: — BRAZIL, São Paulo State: Municipality São Paulo, Hedberg reservoir, from surface sediments, 23º25′55′′S, 47º35′33′′W, 28 August 2014 (Holotype SP! 469240, depicted in Fig. 5 ).

Ecology: Nitzschia pusilluhasta was recorded from 23 samples of the six studied reservoirs. However, considering the quantitative data (see the Material and methods section), this species was registered in 19 samples (six from surface sediments, ten from phytoplankton, and three periphyton), whose limnological conditions ranged from meso to eutrophic (see Table 2 for abiotic characterization).

A higher relative abundance of this species ( Table 4) was registered from surface sediments under eutrophic (Hedberg: 7.0%) than mesotrophic conditions (Itupararanga: 0.9%). In both summer and winter, the highest relative abundance of this species from phytoplankton samples was observed under eutrophic conditions (Hedberg: 1.2% and 1.1%, respectively) and the lowest under mesotrophic conditions (Ipaneminha: 0.2% and 0.2%, respectively).

In the eutrophic reservoir Hedberg, N. pusilluhasta was one of the most abundant taxa (7.0% of relative abundance) in the surface sediments and co-occurred with Aulacoseira ambigua (Grunow) Simonsen (1979: 56) (55.2%), Aulacoseira granulata var. angustissima (Müller) Simonsen (1979: 58) (25.0%) and Aulacoseira granulata (Ehrenberg) Simonsen (1979: 58) var. granulata (20.0%). The most abundant taxa in the phytoplankton of this reservoir were Aulacoseira granulata var. angustissima (64.0%), Navicula rostellata Kützing (1844: 95) (13.0%), and Achnanthidium minutissimum (Kützing) Czarnecki (1994: 157) (5.2%). Nitzschia amphibia , N. gracilis Hantzsch (1860: 40) , N. intermedia Hantzsch ex Cleve & Grunow (1880: 95) , and N. palea (Kützing) W. Smith (1856: 89) also occurred in this reservoir, but they showed a low abundance (<2%).

during summer and winter in the studied reservoirs. Secchi: water transparency, Temp: water temperature, Cond: conductivity,

DO: dissolved oxygen, TN: total nitrogen, TP: total phosphorus, SRS: soluble reactive silica, Chl-a: chlorophyll a.

In the mesotrophic reservoir Ipaneminha, the most abundant species co-occurring with Nitzschia pusilluhasta in the surface sediments were Eunotia intricans Lange-Bertalot & Metzeltin (2009: 141) (28.6%), Discostella stelligera (Cleve & Grunow) Houk & Klee (2004: 208) (42.2%), and Aulacoseira granulata var. angustissima (17.5%). The most abundant species in the phytoplankton of this reservoir were Discostella stelligera (37.4%) and Fragilaria tenera (W. Smith) Lange-Bertalot (1980: 746) (32.5%). Nitzschia acidoclinata Lange-Bertalot (1976: 253) , N. dissipata (Kützing) Rabenhorst (1860: 968) , N. gracilis , N. intermedia , N. palea , N. semirobusta , and N. terrestris (J.B. Petersen) Hustedt (1934: 396) were also registered in this reservoir but with a low abundance (<2%).

In the mesotrophic reservoir Itupararanga, the most abundant taxa in the surface sediments were Aulacoseira ambigua (30.7%) and Aulacoseira granulata var. granulata (15%), whereas in the phytoplankton, the dominant species were Discostella pseudostelligera (Hustedt) Houk & Klee (2004: 223) (47.0%) and Fragilaria spectra Almeida, Morales & Wetzel (2016: 174) (27.1%). Nitzschia acicularis , N. acidoclinata , N. clausii Hantzsch (1860: 40) , N. intermedia , N. palea , N. semirobusta , and N. terrestris , were also present in this reservoir but with a low relative abundance (<2%).

Nitzschia pusilluhasta was also registered from samples of Barra Bonita, Tatu, and Salto Grande reservoirs, but with a low abundance and, therefore, it was not considered in the quantitative analysis.

recorded during summer and winter in Tatu reservoir. Secchi: water transparency, Temp: water temperature, Turb: turbidity,

Cond: conductivity, DO: dissolved oxygen, TN: total nitrogen, TP: total phosphorus, SRS: soluble reactive silica, Chl-a:

chlorophyll a

Figures

FIGURES 2–31. Related species of Nitzschia found in the Nitzschia pusilluhasta sp. nov. type material. 2–21. Nitzschia pusilluhasta sp. nov., LM. 2–17. Valve view. 18–21. Girdle view. Figures 22–26. Nitzschia amphibia. LM. Valve view. Figures 27–31. Nitzschia semirobusta. LM. Valve view. Figures marked with “=” are the same frustules with a different focus. Scale bar = 10 μm.

FIGURES 53–58. Type material of N. pusilluhasta sp. nov., SEM. 53, 54. Valve face in external view. 55. Valve edge showing raphe, first row of areolae, mantle, and pores in the valvocopula. 56. Central portion of valve face, areolae, and raphe. 57. Girdle and valve face views, near the apex showing areolae on valve and mantle, and poroids on the copulae. 58. Apex of the valve showing areolae on the valve face and mantle, raphe, keel and valvocopula poroids. Scale bars: Figs 53, 54 = 5 μm; Fig 55 = 0.5 μm; Figs 56–58 = 1 μm.