Achnanthidium subtilissimum 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 : 161-162

publication ID	https://doi.org/ 10.11646/phytotaxa.405.3.5
persistent identifier	https://treatment.plazi.org/id/03A8A549-FFC7-FFDF-8FBF-FB25FC22FD09
treatment provided by	Felipe
scientific name	Achnanthidium subtilissimum P. Yu
status	sp. nov.

Treatment

Achnanthidium subtilissimum P. Yu , Q-M. You & Q-X Wang sp. nov. ( Figs 293–355 View FIGURES 293–351 View FIGURES 352–355 )

Holotype: SHTU!, slide JZG–201307018, holotype illustrated in Figs 300, 328 View FIGURES 293–351 . 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 based on the narrow valves observed in this new species.

Description: According to LM observations ( Figs 293–347 View FIGURES 293–351 ), valves were linear-elliptical in shape, with wide capitate ends, and valves had a central inflation that was slightly larger in width than the apical expansions. Valve length was 8.5–10.2 μm, and width 2.2–2.8 μm (n =80). Raphe valves possessed a linear-lanceolate axial area with a small oval central area. Rapheless valves possessed a linear-lanceolate axial area that widened toward the middle portion. On both valves, striae are nearly parallel along the entire valve. Striae number was 26–32/10 μm at the center, and up to 32–36/10 μm near the apices on the raphe valve. On the rapheless valve, striae number was 27–30/10 μm in the middle, and up to 30–36/10 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 has single row of linear areolae ( Figs 348 View FIGURES 293–351 , 352 View FIGURES 352–355 ). On the exterior of the raphe valve, the raphe was filiform and straight; proximal raphe ends were straight, and simple; and the distal raphe ends were straight, small and drop shaped and they do not extend on the valve mantle ( Fig. 348 View FIGURES 293–351 ). Striae were uniseriate, comprising 1–3 round or oblong areolae in the entire valve ( Fig. 348 View FIGURES 293–351 ). Some striae had one slit-like areola on the valve mantle ( Fig. 348 View FIGURES 293–351 ). Areolare occlusions were positioned within the opening and could be seen from the exterior ( Fig. 349 View FIGURES 293–351 ). Internally, the raphe terminated distally as an elevated helictoglossa, and the proximal raphe endings were short, deflecting in opposite directions ( Fig. 350 View FIGURES 293–351 ). Areolae were large and round to oblong in shape, and the openings occluded with fine hymenate structures that included small openings around the periphery on the internal valve ( Fig. 351 View FIGURES 293–351 ).

On the external portion of the rapheless valve, the axial area was linear-lanceolate which widened toward the middle portion ( Figs 352, 354 View FIGURES 352–355 ). Striae were uniseriate, comprised of 1–3 transapically-oriented areolae in the middle partition of the valve, and 2–3 irregularly round or small round areolae at the ends ( Fig. 352 View FIGURES 352–355 ). The areolae were occluded with a fine hymen structure velum that could be seen externally ( Fig. 353 View FIGURES 352–355 ). Internally, areolae were round to oblong, and occluded on the valve face, which comprised a fine hymenate structure ( Figs 354–355 View FIGURES 352–355 ).

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 2.8 % relative abundance (total counted, 400 valves) in sample JZG–201307018.

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

Remarks: Achnanthidium subtilissimum can be compared with several species in the same genus, based on similarities in the outline and structure of the valve, including A. acsiae Wojtal, Morales, Vijver & Ector ( Wojtal et al. 2011: 226), A. catenatum (Bily & Marvan) Lange-Bertalot ( Hlúbiková et al. 2011: 23), A. microcephalum Kützing ( Novais et al. 2015: 111), A. sibiricum Kulikovskiv, Lange-Bertalot, Witkowski & Khursevich (Kulikovskiv 2011: 79), A. saprophilum (Kobayashi & Mayama) Round & Bukhtiyarova ( Hlúbiková et al. 2011: 33), A. lineare Smith ( Vijver et al. 2011: 170) and A. lusitanicum Novais & Morais ( Novais et al. 2015: 129). The morphological characteristics of A. subtilissimum and these similar species are summarized in Table 4 to facilitate a comparison. The length of A. subtilissimum does not exceed 10 μm, while other species are longer including A. acsiae (up to 15.8 μm), A. catenatum (up to 17.8 μm), A. microcephalum (up to 14.2 μm), A. saprophilum (up to 14.5 μm), A. lineare (up to 13.5 μm), and A. lusitanicum (up to 13 μm) compared with the new species. Additionally, A. subtilissimum is wider (2.2–2.8 μm) than A. sibiricum (1.7–2.1 μm), but narrower than A. saprophilum (3.0–3.6 μm). Moreover, A. subtilissimum has wide capitate ends and possesses a small oval central area on the raphe valve that is different from other similar taxa. Furthermore, the density of the striae at the apices of A. subtilissimum is higher on both the raphe (32–36/10 μm) and rapheless (30–36/10 μm) valves than in A. catenatum (30–32/10 μm at the apices on the raphe, 30–34/10 μm on the rapheless valve), A. saprophilum (28–31/10 μm on both valves), and A. lineare (28–32/10 μm on both valves). The density of striae in the new species is lower than in A. acsiae (36–38/10 μm at the apices on the raphe valve and 38/10 μm on the rapheless valve), and A. lusitanicum (40/10 μm at the apices on the raphe valve). Additionally, fewer areolae per striae are present on A. subtilissimum on both valves (1–3) than in A. acsiae (3–4 on both valves), A. catenatum (5–6 on the raphe valves, 4–5 on the rapheless valves), A. microcephalum (2–5 on the raphe valves, 3–4 on the rapheless valves), and A. microcephalum (2–5 on the raphe valves, 3–4 on the rapheless valves).