Gomphonema frequentiformis (Metzeltin & Krammer) C.E.Wetzel & F.F.Almeida, 2020

De Almeida, Fabiane F., Ector, Luc, Silva, Edinaldo Santos & Wetzel, Carlos E., 2020, Gomphonema frequentiformis (Metzeltin & Krammer) comb. nov. (Bacillariophyta): ecology and taxonomy of a Neotropical diatom, Phytotaxa 439 (3), pp. 265-275 : 270-272

Gomphonema frequentiformis (Metzeltin & Krammer) C.E.Wetzel & F.F.Almeida comb. nov. (LM, Figs. 3−17 , SEM, Figs 19−29 )

Basionym :— Encyonopsis frequentiformis Metzeltin & Krammer in Metzeltin & Lange-Bertalot 1998, I conographia Diatomologica vol. 5, p. 39, pl. 137, figs 13, 14, pro parte (nec figs 11, 12).

Lectotype: Prep. AmS-351B in Coll. Lange-Bertalot, Bot. Inst. der J.W. Goethe-Universitat, Frankfurt am Main.

Type locality:— Venezuela, small stream in Roraima Mountains, 12 km vor Paray Tepuy, leg. Julio Schneider, 31.3.1994.

Morphology: — LM ( Figs 3−17 ): Valves lanceolate, heteropolar (footpole raphe longer than headpole raphe), not dorsiventral. Both apices strongly capitate. Valve length 28–38 μm; valve width 7.5–9.5 μm. Axial area narrow. The central area is symmetrical with a single long stria on one side terminating in a distinct small rounded isolated pore sunk into the valve face. Striae slightly radiate, becoming parallel near the apices, 15–16 in 10 μm. A sinuous central raphe system with proximal ends weakly expanded and deflected towards the isolated pores. SEM ( Figs 19−29 ): Externally smooth valve face with small round shallow depressions along the axial area ( Fig. 19 ). Uniseriate striae formed by sigmoid-elongated areolae apically orientated, striae continuous between the valve face and the mantle, mantle shallow; isolated pore aperture round ( Fig. 21 ). Internal proximal raphe ends hook-shaped towards the same size. The internal opening of the isolated pore is transversely elongated. The internal areolar openings are small, round to elongated, located in shallow foraminal row. Specimens usually have two apical pore fields (headpole and footpole), sometimes less evident on the headpole ( Fig. 37 ) and consist of dense concentration of sigmoid pores, with similar shape to the valve face, but much smaller ( Figs 24–27 ). Helictoglossae are well developed and short pseudosepta are present at both apices ( Figs 28–29 ).

Ecology and distribution: — Gomphonema frequentiformis was commonly found in the samples from the Negro River. In a set of 87 periphytic samples collected between 2013 and 2014, the species was present in all sampling stations independently of the area (i.e. low, intermediate and high anthropogenic impact). However, it was the most abundant species reaching 48% at sampling station n° 9 on the date of June 22, 2014 ( Fig. 1 ). Other taxa associated to G. frequentiformis in this sample included: Eunotia amazonica F.F.Almeida & C.E.Wetzel in Almeida et al. (2018: 169), E. bilunaris (Ehrenberg) G. Schaarschmidt (1881: 159) , E. intricans Lange-Bertalot & Metzeltin (2009: 141– 142) , E. parasiolii Metzeltin & Lange-Bertalot (1998: 72–73) , E. rabenhorstiana (Grunow) Hustedt (1949: 72) , Fragilariforma amazonica C.E.Wetzel, P.D.Almeida & Ector in Almeida et al. (2017: 280), Frustulia saxoneotropica Metzeltin & Lange-Bertalot (2007: 142) and Gomphonema archaevibrio Lange-Bertalot & E.Reichardt in Reichardt (1995: 32). Based on physico-chemical characteristics of water measured in the sampling station ( Table 1) and the localization of the station n° 9 in this study (HAI – high anthropogenic influence area (see also Almeida et al. 2018), we can say that G. frequentiformis prefers organically polluted sites in the Rio Negro. This assertion is also supported by data presented in Wetzel (2011), which during an expedition across the Negro River basin in March 2005 collected 129 samples of periphyton mainly in riparian flooded forests located in nine different tributaries spread over about 800 km of Negro River. Gomphonema frequentiformis was identified in this study as Encyonopsis frequentis and had its greatest relative abundance values into the most organically polluted sites investigated. The species has been reported only a few times outside its type locality: in a previous report by Silva (2009) for the central region of Brazil, while Marra et al. (2016) observed the species as epiphytic in urban reservoirs of the Paraná state, south Brazil.

Figures

FIGURE 1. A) Distribution of Gomphonema frequentiformis comb. nov. in South America; B) Sampling sites located on the left bank of the Negro River, in the vicinity of Manaus city, Brazilian Amazon; C) Distribution of Gomphonema frequentiformis in the sampling stations 1 to 12 at Manaus (AM, Brazil).

FIGURES 2–17. Gomphonema frequentiformis comb. nov. LM. Fig. 2. Raphe length measures taken from the helictoglossa at the apical pole (A) and footpole (B) until central raphe endings. Figs 3–17. Size reduction series of a population from the Negro River. Fig. 18. Boxplot results of paired measurements taken (n=30). T-test two-tailed P <0.0001, considered extremely significant different. Scale bar = 10 µm.

FIGURES 19–29. Gomphonema frequentiformis comb. nov.SEM.Fig.19. External valve outline overview.Sinuous raphe and heteropolar valves. Fig. 20. Internal valve. Fig. 21. Detail of central area showing rounded isolated pore (‘stigma’) and sigmoid slit-like areolae. Striae not interrupted in the valve face-mantle junction. Proximal raphe endings rounded. Figs 22–23. Internal detail of central area showing transversely elongated isolated pore located in a long groove. Strongly hook-shaped proximal raphe ending.Areolar openings are large and round without internal occlusions, located in а deep foraminal row between strongly silicified vimines. Figs 24–27. Detail of apical (24, 25) and footpoles (26, 27) showing the presence of apical pore field on both apices. Raphe slightly curved to the same side. Figs 28–29. Internal detail of both apices showing the helictoglossae and the slit-like internal areolae openings. Note the pseudoseptum present at both apices (a silica plate extending internally from the apical portion of the valve). Scale bars = 10 µm (Figs 19, 20), 4 µm (Fig. 21), 3 µm (Figs 24–27), 2 µm (Figs 22, 23, 28, 29).

FIGURES37–40.Common Gomphonemaspeciesfromthe RioNegrobasin(BrazilianAmazon).Figs 37–38.Gomphonemafrequentiformis showing external valve overview and detail of the central area with slit-like areolae and apical pore field conspicuous on the footpole. Figs 39–40. Gomphonema archaevibrio showing slight heteropolarity and dorsiventrality. Detail of the central area showing sigmoid slit-like areolae as well. Scale bars = 30 µm (Fig. 39), 10 µm (Fig. 37), 5 µm (Figs 38, 40).