Brachysira altepetlensis D.Mora, R.Jahn & N.Abarca, 2017

Mora, Demetrio, Carmona, Javier, Jahn, Regine, Zimmermann, Jonas & Abarca, Nelida, 2017, Epilithic diatom communities of selected streams from the Lerma-Chapala Basin, Central Mexico, with the description of two new species, PhytoKeys 88, pp. 39-69 : 41

Brachysira altepetlensis D.Mora, R.Jahn & N.Abarca sp. nov. Figs 118-132

Holotype.

B 40 0042006; Figure 121 represents the holotype.

Isotypes.

B 40 0042007 (SEM stub), QMEX DIAT0001 (Slide).

Cleaned unmounted material is available under the numbers B 40 0042008 and QMEX DIAT0002.

Type locality.

Paredones stream, on the outskirts of Paredones village, Dolores Hidalgo, Guanajuato, Mexico (21°11'20.60"N; 101°06'53.40"W; 2089 m a.s.l). Collected by Demetrio Mora on 07.09.2014.

Registration.

http://phycobank.org/100101

Description.

the valves are lanceolate to linear-lanceolate with rostrate apices. The axial area is narrow-linear throughout the valve and the central area round to elliptical (Figs 118-128 ). Length: 12.6-23.1 µm, width: 3.2-4.5 µm, length/width ratio: 3.2-5.4; striae in 10 µm: 34-37. The raphe is filiform, slightly sinuous, bordered by a thickened longitudinal siliceous rib on both sides (Figs 129-131 ). The proximal raphe ends are straight, while the distal raphe endings are T-shaped (Figs 129-131 ). Internally, the proximal raphe endings are slightly bent to the same side of the valve and distally end in helictoglossa (Fig. 132 ). The striae are uniseriate and radiate throughout; composed of 2-3 transapically elongated areolae except close to the apices where only one elongated areola is present (Figs 129-131 ). Striae in the valve mantle are composed of single elongated areola (Fig. 131 ). In some valves the Voigt discontinuity can be seen (Fig. 132 ). Internally the areolae are occluded by hymens (Fig. 132 ). The virgae have irregularly spaced papillae (Figs 129-131 ).

Differential diagnosis.

Brachysira procera Lange-Bertalot & Gerd Moser is the species which most closely resembles B. altepetlensis in valve outline but is larger (25-60 µm), wider at valve center (4.5-6 µm) and has less striae in 10 µm (27-30) ( Lange-Bertalot and Moser 1994). The valve outline of Brachysira neglectissima Lange-Bertalot also resembles that of B. altepetlensis but the valves of B. neglectissima are wider (4.3-4.5 µm), have more striae (36-40), the areolae are arranged in a way that they give the appearance of waves and each single areola is comparatively not as elongated as in B. altepetlensis ( Lange-Bertalot and Moser 1994). Brachysira guarrerai Vouilloud, Sala & Núñez-Avellaneda is also similar in valve outline but the valves are wider (5.5-7 µm), have less striae (26-32) and lack papillae in the interstriae ( Vouilloud et al. 2014).

The valve dimensions as well as the striae density of the new species fall within the range of the Brachysira neoexilis Lange-Bertalot species complex, but the type population of B. neoexilis has clear capitate apices and the larger specimens have a very slightly triundulate valve margins ( Lange-Bertalot and Moser 1994). All the other populations from B. neoexilis species complex depicted in the original description ( Lange-Bertalot and Moser 1994) have subcapitate to capitate apices, not matching at all the outline of B. altepetlensis . The specimens depicted in Rumrich et al. (2000), identified as B. neoexilis (Pl. 89: figs 18-20), closely resemble B. altepetlensis in valve outline but they clearly differ from specimens depicted in the type description of B. neoexilis ( Lange-Bertalot and Moser 1994). The specimens of Brachysira found by Abarca-Mejía (2010) in a spring also in the Lerma-Chapala Basin, closely resemble B. altepetlensis in LM, but her identification was based on Rumrich et al. (2000), which led her to identify those valves as B. neoexilis .

Etymology.

this new Brachysira species takes the name from the word “āltepētl” which means "water mountain" in Náhuatl language, that is how the surrounding mountains were used to be named by native people 500 years ago, at the time Spaniards first came to the region.

Distribution.

apart from the type locality, this species was also found in four streams sampled for this study, namely Peña Colorada (site 4), San Martín (site 5), La Laborcilla 1 (site 7) and La Laborcilla 2 (site 8), all of these sites were characterized by low specific conductivity (≤ 100 μS /cm) and pH values going from acidic to slightly alcaline (5.1-7.9). But B. altepetlensis only reached high relative abundances (>10%) in acidic waters (pH= 5.1-5.8) with low specific conductivity (42-53 μS /cm).

Figures

Figures 118 - 132. Brachysira altepetlensis D. Mora, R. Jahn & N. Abarca, sp. nov. LM (118 - 128) and SEM (129 - 132). 118 - 123 type material, from Paredones stream, Guanajuato, Mexico, collected on 07.09.2014 121 designated as holotype 124 - 125 collected from type location but on 06.10.2013 126 - 128 collected from type location but on 09.02.2014 129 - 132 from type material: 129 - 130 external view of entire valves 131 external view of an entire valve showing elongated areolae in the valve mantle 132 internal view of entire valve, showing occlusion of the areolae by hymens. The arrow points at Voigt discontinuity. Scale bars 10 μm (118 - 128); 5 μm (129 - 132).