Achnanthidium jiuzhaienis 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 : 149-152

Achnanthidium jiuzhaienis P. Yu , Q-M. You & Q-X Wang sp. nov. ( Figs 2–129 )

Holotype: SHTU! slide JZG–1307027, holotype illustrated in Figs 12, 41 . Diatom samples are housed in the Biology Department Diatom Herbarium, Shanghai Normal University, China.

Isotypes: COLO!, slide 628094, 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°09’34”N, 103°52’39”E, altitude: 2432 m, collected by Q.X. Wang, on July 5, 2013.

Etymology: Species was named for the Jiuzhai Valley Nature Reserve where the samples were collected.

Description: According to LM observations ( Figs 2–97 ), valves were wide lanceolate with subcapitate to capitate ends. The raphe valve was concave and the rapheless valve was convex. Valve length was 19–40 μm, width was 3.2– 4.5 μm (n =200). Both valves possessed a narrowly linear-lanceolate axial area that widens slightly towards the middle portion; a differentiated central area was absent. On both valves, striae radiate to nearly parallel. Striae number was 22–28/10 μm at the center, and up to 30–38/10 μm near the apices on the raphe valve. On the rapheless valve, striae were 22–27/10 μm in the middle and 28–36/10 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 ( Figs 98 , 106 , 115 , 123 ). The mantle had a single row of linear areolae ( Figs 100 , 108 , 125–126 ). On the raphe valve, externally, the raphe were filiform and straight (Figs 98,115). The external terminal raphe fissures hooked toward the same side of the valve ( Figs 98 , 115 ). The proximal raphe endings slightly expanded ( Figs 101 , 118 ). Striae were comprised of 2–5 transapically-oriented areolae in the middle portion ( Figs 101 , 118 ) and 1–3 transapically-oriented areolae at the apices ( Figs 100 , 117 ). Internally, the raphe terminated distally as an elevated helictoglossa ( Figs 99, 102 , 116, 119 ), and the proximal raphe endings gently deflecting in opposite directions ( Figs 103 , 120 ). Areolae appeared to be oblong, and the openings occluded with fine hymenate structures that included small openings on the periphery and a central occlusion ( Figs 104–105 , 121–122 ).

On the rapheless valve, the axial area had raphe vestiges at the apices ( Figs 106, 108–109 , 123, 125–126 ). Striae consisted of 2–5 transapical slit-like areolae at the middle portion ( Figs 110–111 , 127, 129 ), becoming 1–3 irregular transapical slit-like areolae at the apices ( Figs 108–109 , 125–126 ). Internally, the raphe vestiges at the apices consisted of 1–2 openings or absent ( Figs 107, 112–113 , 124, 128 ). The shape of areolae were internally oblong, and areolar openings had fine hymenate occlusions ( Figs 114 ).

Ecology: Collected in one sample, JZG–201307027, on filamentous algae (pH 8.4, water temperature 9.8 °C, TDS 0.246 g /L, conductivity 367 μs/cm). This new species occurred at 4.3 % relative abundance (total counted, 400 valves) in sample JZG–201307027. There were 6 species that accounted for more than 5 % of this sample: Cymbella vulgata Krammer ( Krammer 2002: 55) (19 %), Delicata delicatula (Kützing) Krammer ( Krammer 2003: 113) (17.3 %), Achnanthidium minutissimum (Kützing) Czarnecki (10.8 %), Denticula elegans Kützing ( Kützing 1844: 44) (9.3 %), Achnanthidium pyrenaicum (Hustedt) Kobayasi (6%), and Achnanthidium macrocephalum (Hustedt) Round & Bukhtiyarova ( Round & Bukhtiyarova 1996: 75) (5.8 %).

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

Remarks: Achnanthidium jiuzhaienis can be compared to several species in the same genus, based on similarities in the outline and structure of the valve, including A. gracillimum (Meister) Lange-Bertalot ( Meister 1912: 234, Krammer & Lange-Bertalot 2004: 430), A. acerosum Vijver, Lange-Bertalot & Jarlman ( Vijver et al. 2011: 198), and A. ertzii Vijver & Lange-Bertalot ( Vijver et al. 2011: 200). The morphological characteristics of A. jiuzhaienis . and these similar species are summarized in Table 1 to facilitate a comparison. In terms of features viewed with an LM, the outline of the valves of A. jiuzhaienis . were wide lanceolate with subcapitate to capitate ends, while that of A. gracillimum were linear-lanceolate with broadly rounded ends, A. acerosum were narrowly lanceolate with subcapitate ends, and A. ertzii is linear-lanceolate with capitate ends. Additionally, the valves of A. jiuzhaienis were longer (19–40 μm) than the valves of A. acerosum (15–19 μm) and A. ertzii (18–22 μm), as well as wider (3.2–4.5 μm) compared to ( A. gracillimum (3–4 μm), A. acerosum (1.9–2.4 μm), and A. ertzii (2.2–2.8 μm). No central area was observed in the new species, but the other species did have a central area. With respect to features observed with an SEM, A. jiuzhaienis . was distinguished from these similar species by the presence of hooked external distal raphe fissures; the external distal raphe ends were straight in A. acerosum and A. ertzii .

Two morphotypes appeared to be present in this population of A. jiuzhaienis . One morphotype was longer with subcapitate ends ( Figs 2–49 ), while the other morphotype was shorter with capitate ends ( Figs 50–97 ). Additionally, on the raphe valve, striae radiated in the middle portion in the longer morphotype ( Figs 115, 118 ), and were nearly parallel in the shorter morphotype ( Figs 98, 101 ).

Figures

FIGURES 2–97. Achnanthidium jiuzhaienis sp. nov., LM. 12, 41. Holotype; 2–49. Longer morphotype, (2–25) Raphe valves; (26–49) Rapheless valves; 50–97. Shorter morphotype, (50–73) Raphe valves; (74–97) Rapheless valves. Scale bar 10 μm.

FIGURES 98–105. Achnanthidium jiuzhaienis sp. nov. Longer morphotype, SEM views of raphe valve. 98. External view of an entire raphe valve. 99. Internal view of an entire raphe valve. 100–101. Details of the apices and the central area on the external of the raphe valve. 102–103. Detail of the apices and the central area on the internal of the raphe valve. 104–105. Internal areola openings with fine hymenate structures. Scale bars 5 μm (98–99), 1 μm (100–103), 0.2 μm (104–105).

FIGURES 106–114. Achnanthidium jiuzhaienis sp. nov. Longer morphotype, SEM views of rapheless valve. 106. External view of an entire rapheless valve. 107. Internal view of an entire rapheless valve. 108–109. Raphe vestiges at the two apices of the same valve. 110. Detail of the central area on the external of the rapheless valve. 111. Detail of the central area on the internal of the rapheless valve. 112–113. Raphe vestiges at the apices with usually 1–2. 114. Internal areola openings with fine hymenate structures. Scale bars 5 μm (106–107), 1 μm (108–113), 0.2 μm (114).

FIGURES 115–122. Achnanthidium jiuzhaienis sp. nov. Shorter morphotype, SEM views of raphe valve. 115. External view of an entire raphe valve. 116. Internal view of an entire raphe valve. 117–118. Details of the apices and the central area on the external of the raphe valve. 119–120. Detail of the apices and the central area on the internal of the raphe valve. 121–122. Internal areola openings with fine hymenate structures. Scale bars 5 μm (115–116), 1 μm (117–120), 0.2 μm (121–122).

FIGURES 123–129. Achnanthidium jiuzhaienis sp. nov. Shorter morphotype, SEM views of rapheless valve. 123. External view of an entire rapheless valve. 124. Internal view of an entire rapheless valve. 125–126. Raphe vestiges at the two apices of the same valve. 127. Detail of the central area on the external of the rapheless valve. 128. Raphe vestiges at the apices. 129. Detail of the central area on the internal of the rapheless valve. Scale bars 5 μm (123–124), 1 μm (125–129).