Achnanthidium limosua P. Yu

Yu, P., You, Q-M., Pang, W-T., Cao, Y. & Wang, Q-X., 2019, Five new Achnanthidiaceae species (Bacillariophyta) from Jiuzhai Valley, Sichuan Province, Southwestern China, Phytotaxa 405 (3), pp. 147-170 : 158-160

Achnanthidium limosua P. Yu , Q-M. You & Q-X Wang sp. nov. ( Figs 232–292 )

Holotype: SHTU!, slide JZG–201307018, holotype illustrated in Figs 242, 273 . Diatom samples are housed in the Biology Department Diatom Herbarium, Shanghai Normal University, China.

Isotypes: COLO!, slide 614007, Samples are housed in the Kociolek Collection, University of Colorado, Museum of Natural History Diatom Herbarium, Boulder, U.S.A.

Type locality: CHINA. Samples collected from Jiuzhai Valley Nature Reserve, Sichuan Province, 33°09’43”N, 103°53’34”E, altitude: 2332 m, collected by Q.X. Wang, on July 5, 2013.

Etymology: Species was named after the diatom species collected on sediment.

Description: According to LM observations ( Figs 232–285 ), valves were linear-elliptical in shape, with subcapitate apices. Valve length was 7.4–11.4 μm, and width 3.2–4 μm (n =100). Raphe valves possessed a linear axial area with a small oval central area. Rapheless valves possessed a narrowly linear-lanceolate axial area that widened slightly toward the middle portion. On both valves, striae slightly radiated along the middle portion and become radiated more near the apices. Striae number was 26–30/10 μm at the center, and up to 35–40/10 μm near the apices on the raphe valve. On the rapheless valve, striae were denser toward the valve apices, 27–32/10 μm in the middle and 32–40/10 μm near the apices. Individual areolae were not visible with an LM.

SEM observations of both valves revealed that the valve face: had a mantle junction bordered by a narrow hyaline area and the mantle had a single row of linear areolae ( Figs 286 , 290 ). On the exterior of the raphe valve, the raphe was filiform and straight, proximal raphe ends were straight, and simple, while the distal raphe ends were straight and extended on the valve mantle ( Fig. 286 ). Striae were uniseriate, comprised of 2–4 oblong areolae in the middle portion, and 1–3 irregularly-round or oblong areolae elsewhere ( Fig. 286 ). One slit-like areola occasionally appeared at the end of the striae close to the valve margin ( Fig. 286 ). Areolae occlusions were positioned within the opening and could be seen from the exterior of the internal valve ( Fig. 287 ). Internally, the raphe terminated distally as an elevated helictoglossa, and the proximal raphe endings were short, deflecting in opposite directions ( Fig. 288 ). Areolae were large and irregularly-round to oblong in shape, while the openings occluded with fine hymenate structures that included small openings around the periphery ( Fig. 289 ).

On the rapheless valve, externally, the axial area was linear-lanceolate that widens slightly toward the middle portion ( Fig. 290 ). Striae were uniseriate, comprised of 4–5 oblong to transapically elongated areolae in the middle partition of the valve, and 1–3 irregularly round or transapically elongated areolae at the ends ( Fig. 290 ). The areolae occluded with fine hymen structures that could be seen externally ( Fig. 291 ).

Ecology: Collected in one sample JZG–201307018 on sediment (pH 8.42, water temperature 9.9 °C, TDS 0.246 g /L, conductivity 367 μs/cm). This new species occurred at 2.5 % relative abundance (total counted 400 valves) in sample JZG–201307018. There were 5 species that accounted for more than 5 % of this sample: Staurosirella ovata Morales (30.3 %), Staurosira venter (Ehrenberg) Cleve & Moller ( Cleve & Möller 1879: 242) (20 %), Pseudostaurosira brevistriata var. inflata (Pantocsek) Edlund ( Edlund 1994: 12) (18.8 %), Achnanthidium straubianum Lange-Bertalot (6.5 %), and Encyonema silesiacum (Bleisch) Mann ( Round et al. 1990: 667) (6 %).

Distribution: thus far, the new species was collected only at the type locality in Jiuzhai Valley.

Remarks: Achnanthidium limosua can be compared to several species in the same genus, based on similarities in the outline and structure of the valve, including A. lusitanicum Novais & Morales ( Novais et al. 2015: 129), A. eutrophilum Lange-Bertalot ( Hlúbiková et al. 2011: 30), A. caravelense Novais & Ector ( Novais et al. 2011: 142), A. acsiae Wojtal, Morales et al. ( Wojtal et al. 2011: 226), and A. minutissimum (Kützing) Czarnecki ( Morales et al. 2011: 97). The morphological characteristics of A. limosua and these similar species are summarized in Table 3 to facilitate comparison. Valves of A. limosua are wider (3.2–4.0 μm) than A. subtilissimum P. Yu , Q-M. You & Q-X Wang (2.2–2.8 μm), A. lusitanicum (2.3–3.0 μm), A. acsiae (7.0–15.8 μm), and A. minutissimum (3.0–3.5 μm), but narrower than A. eutrophilum (to 5.8 μm). Additionally, on the raphe valves of A. limosua possess a linear axial area, while the axial area is linear-lanceolate in A. subtilissimum , A. eutrophilum , and A. minutissimum . Moreover, A. limosua has a small oval central area, while A. caravelense has a round to elliptical central area, and A. lusitanicum , A. eutrophilum , and A. acsiae have a rectangular fascia central area. Furthermore, on the rapheless valve, the new species had no central area, but A. caravelense and A. lusitanicum possess an elliptical central area, while A. minutissimum has an elliptical to lanceolate central area. Additionally, the density of striae at the apices of A. limosua is higher on both the raphe (35–40/10 μm) and rapheless (32–40/10 μm) valves than in A. lusitanicum (30–35/10 μm on the rapheless valve), A. eutrophilum ( Hlúbiková et al. 2011) (25–30/10 μm on the rapheless valve), and A. minutissimum ( Morales et al. 2011) (22–24/10 μm on raphe valve, 24–30/10 μm on the rapheless valve).

Figures

FIGURES 232–289. Achnanthidium limosua sp. nov. 232–259. LM of raphe valve. 260–285. LM of rapheless valve. 242, 273. Holotype. 286–289. SEM views of raphe valve. 286. External view of an entire raphe valve. 287. Detail of the areolae on the external of the raphe valve. 288. Internal view of an entire raphe valve. 289. Internal areola openings with fine hymenate structures. Scale bars 10 μm (232– 285), 1 μm (286, 288), 0.1 μm (287, 289).

FIGURES 290–292. Achnanthidium limosua sp. nov. SEM views of rapheless valve. 290. External view of an entire rapheless valve. 291. Detail of the areolae on the external of the rapheless valve. 292. Internal view of an entire rapheless valve. Scale bars 1 μm (290, 292), 0.1 μm (291).