Gomphonema mutunensis Ruwer, Ludwig

Ruwer, Daiane T., Ludwig, Thelma A. V. & Rodrigues, Liliana, 2019, Two new diatom species (Bacillariophyceae) from Brazilian floodplain: Actinella hermes-moreirae sp. nov. and Gomphonema mutunensis sp. nov., Phytotaxa 395 (2), pp. 71-80 : 75-77

Gomphonema mutunensis Ruwer, Ludwig & Rodrigues, sp. nov. ( Figs 32–47 , 48–55 )

Frustule rectangular in lateral view. Valves lanceolate, headpole rostrate to sub-rostrate, sometimes apiculate, footpole attenuated-rounded. Length 22.5-47.9 μm, breadth 5.9-7.9 μm (n=30). Axial area linear. Central area unilateral, delimited by shorter striae. Stigma located at the end of central stria, rounded externally and elongated internally. Raphe straight with proximal ends nearly straight, not dilated, slightly bent to stigma side. Terminal ends of raphe curved. Striae uniseriate, radiate, more spaced at center. Areolae occasionally visible but usually difficult to resolve in LM, C-, S-, 3-shaped. Stria density 13-16 in 10 μm, composed by 6-7 areolae in 2 μm. Bilobed pore field present at footpole.

Type:— BRAZIL. Paraná: Porto Rico, Ilha Mutum, Upper Paraná River Floodplain, swamp, periphyton, 22°45’31.98”S, 53°17’52.60”W, April 2016, D. T. Ruwer (holotype UPCB! 78281, here illustrated in Fig. 40 ).

Etymology: —The specific epithet refers to the place ‘Mutum Island’ where species was found.

Material examined: — BRAZIL. Paraná: Porto Rico, Ilha Mutum , periphyton, 12-IV-2016, Ruwer et al. (78280 UPCB, 78281 UPCB) ; sediment, 27-II-2012,Ruwer et al. (78283 UPCB,78287 UPCB, 78291 UPCB,78295 UPCB - 78298 UPCB, 78300 UPCB - 78302 UPCB, 78304 UPCB, 78314 UPCB) .

Gomphonema mutunensis sp. nov. ( Fig 40 ) is very similar to members of the type of Gomphonema parvulum (Kützing) Kützing (1849: 65) and morphotypes from Abarca et al. (2014), by sharing the rostrate to sub-rostrate headpole ( Abarca et al. 2014) ( Table 2). Morphotypes from the G. parvulum complex differ mainly by the areolae and the stigma shapes, features better observed by electron microscopy (Kützing 1849, Reichardt 1999, Abarca et al. 2014). Since light microscopy is often not enough to observe those frustule details, comparing similar taxa became difficult as some species have not had these features documented ( Kociolek & Stoermer 1993).

Levkov et al. (2016) illustrated G. parvulum morphotype 2, which appears to be the most similar taxa to G. mutunensis , differing by the shape of the footpole and the striae density ( Table 2). Gomphonema jadwigiae Lange-Bertalot & Reichardt (1996: 70) and G. exilissimum Lange-Bertalot & Reichardt (2016: 70) also present similar valve dimensions to G. mutunensis . G. exilissimum is at the lower end of valve measurement ranges and less protracted rostrate headpoles. G. jadwigiae differs in headpole morphology (shortly rostrate to apiculate, sometimes truncated) and the slit-shaped areolae ( Lange-Bertalot & Metzeltin 1996, Levkov et al. 2016) ( Table 2). Therefore, G. mutunensis sp. nov. is distinguished among Gomphonema taxa by headpole rostrate to sub-rostrate rounded, areolas with different shapes and external central raphe ending not drop-like ( Table 2).

Despite the large number of diatom records for Brazil and for Upper Paraná River floodplain (almost more than 150 species, Dunck et al. 2018), further taxonomic studies should be conducted in the floodplain system, due to the importance of this ecological system in the maintenance and conservation of local biodiversity, which has been threatened by man-made impacts. As also due to the large number of areas still taxonomically unexplored in the floodplain. The lack of taxonomic studies has led to the propagation of many errors in taxonomy and identification. Therefore, taxonomic studies contribute to the knowledge of the actual distribution of species, as well as the misidentified identification of species. Thus, we believe that G. mutunensis sp. nov. and A. hermes-moreirae sp. nov. may have an even greater distribution. Through this work, we also emphasize the need for analysis of sedimentary samples for the contribution of diatom biodiversity. The peculiar features observed in A. hermes-moreirae sp. nov. and G. mutunensis sp. nov., clearly distinguished the proposed species from other allied taxa. This show the great contribution of this work to the knowledge of the biodiversity of the floodplain.

Figures

FIGURE 32–47. Gomphonema mutunensis sp. nov. LM. Valve view from type material. Scale bar = 10 μm.

FIGURE 48–51. Gomphonema mutunensis sp. nov. from type material, Mutum Island, SEM. 48-51. Internal and external view of valve, respectively. Scale bar = 10 μm. 50. Internal view of axial area. 51. External view of axial area showing the central stigma (arrow). Scale bar = 2 μm.

FIGURE 52–55. Gomphonema mutunensis sp. nov. from type material, Mutum Island, SEM. 52. Girgle view. Scale bar = 10 μm. 53. Aspect of striae and areola shape. Scale bar = 2 μm. 54. Footpole in external view showing the pore field (arrow). 55. Headpole in external view. Scale bar = 1 μm.