Achnanthidium epilithica 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 : 154-157

Achnanthidium epilithica P. Yu , Q-M. You & Q-X Wang sp. nov. ( Figs 130–231 )

Holotype: SHTU!, slide JZG–201307043, holotype illustrated in Figs 158, 217 . Diatom samples are housed in the Biology Department Diatom Herbarium, Shanghai Normal University, China.

Isotypes: COLO!, slide 614008, 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°11’40”N, 103°53’34”E, altitude: 2250 m, collected by Q.X. Wang, on July 7, 2013.

Etymology: Species was named after the diatom species collected on the face of stones and dead wood.

Description: According to LM observations ( Figs 130–222 ), valves were linear-elliptical to elliptical in shape, with broadly rounded ends. Valve length was 9.3–21.3 μm, and width 3.3–5.3 μm (n =200). Both valves possessed a linear axial area, and the central area was in a bow tie shape. Striae radiated along the entire valve. Striae number was 22–28/10 μm at the center, and up to 25–34/10 μm near the apices on the raphe valve. On the rapheless valve, striae radiated along the middle portion and were nearly parallel near the apex, becoming denser toward the valve apices, as well as 26–30/10 μm in the middle and 30–35/10 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 wider hyaline area ( Figs 223 , 227–228 ), and the mantle had a single row of linear areolae ( Figs 223 , 227 ). 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 did not extend on the valve mantle ( Fig. 223 ). Striae were uniseriate, comprised of 1–3 oblong areolae or transapically-oriented areolae in the center of the valve, with 1–2 large, irregularly-round, or transapically-oriented areolae elsewhere ( Fig. 223 ). One slit-like areola occasionally appeared at the end of the striae close to the valve margin ( Fig. 223 ). Areolae occlusions are positioned within the opening and could be seen from the exterior ( Fig. 225 ). Internally, the raphe terminated distally as an elevated helictoglossa, and the proximal raphe endings were short, deflecting in opposite directions ( Fig. 224 ). Areolae were large and irregularly-round to oblong in shape and the openings are occluded with fine hymenate structures that included small openings around the periphery ( Fig. 226 ).

On the external side of the rapheless valve, the axial area was linear, and possessed a bow tie-shaped central area ( Figs 227–228 ). Striae were uniseriate, comprised of 1–3 round to transapically elongate areolae in the middle portion of the valve, and 1–2 irregularly round or transapically elongate areolae at the ends ( Fig. 228 ). One slit-like areola occasionally appeared at the end of the striae close to the valve margin ( Figs 227–228 ). The areolae were occluded with a fine hymen structure that could be seen externally ( Fig. 230 ). Internally, areolae were round to transapicallyelongated, occluding on the valve face and mantle, and the occlusions comprised a fine hymenate structure ( Figs 229, 231 ).

Ecology: Collected in two samples: JZG–201307008 on dead wood (pH 8.4, water temperature 8.2 °C, TDS 0.198 g /L, conductivity 296 μs/cm); and JZG–201307043 on stones (pH 8, water temperature 12.8 °C, TDS 0.227 g /L, Conductivity 338 μs/cm).The samples of this new species occurred at 5.5 % and 4.5 % relative abundance (total counted 400 valves) in samples JZG–201307008 and JZG–201307043, respectively. There were 7 species that accounted for more than 5 % of sample JZG–201307008: Denticula elegans Kützing ( Kützing 1844: 44) (29.3 %), Delicata delicatula (Kützing) Krammer (18 %), Adlafia bryophila (Petersen) Lange-Bertalot ( Moser et al. 1998: 89) (9 %), Staurosirella ovata Morales ( Morales & Manoylov 2006: 357) (6.5 %), Achnanthidium minutissimum (Kützing) Czarnecki (5.8 %), Encyonopsis descripta (Hustedt) Krammer ( Krammer 1997: 123) (5.5 %), and Achnanthidium epilithica sp. nov. (5.5 %). There were 4 species that accounted for more than 5 % at sample JZG–201307043: Denticula elegans Kützing (30.8 %), Delicata delicatula (Kützing) Krammer (26.8 %), Encyonopsis descripta (Hustedt) Krammer (18.8 %), and Adlafia bryophila (Petersen) Lange-Bertalot (13.3 %).

Distribution: thus far, the new species was only collected only from the two sampling localities in Jiuzhai Valley.

Remarks: Achnanthidium epilithica can be compared to several species in the same genus, based on similarities in outline and structure of the valve, including A. dolomiticum Cantonati & Lange-Bertalot ( Cantonati & Lange-Bertalot 2006: 1185), A. subexigua Hustedt ( Krammer & Lange-Bertalot 2004: 40), and A. straubianum Lange-Bertalot ( Hlúbiková et al. 2011: 37). The morphological characteristics of A. limosua and these similar species are summarized in Table 2 to facilitate comparison. The overall lengths of individuals of the three species do not typically exceed 16 μm, and their widths are less than 4.5 μm, while A. epilithica was longer (21.3 μm) and wider (up to 5.3 μm) than the three similar taxa. On the exterior of the valve, the mantle junction of A. epilithica was bordered by a wider hyaline area, while the similar species have a narrow hyaline area. Furthermore, both valves of A. epilithica possess a bow tie-shaped central area, while the central area of A. dolomiticum has a narrow fascia on the raphe valve and rectangular to lanceolate on the rapheless valve, A. subexigua has a bow tie-shaped central area in the raphe valve, and A. straubianum has a central area that is entirely absent. Additionally, on the rapheless valve, A. epilithica possess a linear axial area, while A. subexigua has a lanceolate to rhombus-lanceolate axial area. A. epilithica appears to be clearly different from the three similar Achnanthidium species based on its bow tie-shaped central area of both valves and dense striation.

Figures

FIGURES 130–222. Achnanthidium epilithica sp. nov., LM. 158, 217. Holotype; 130–176. Raphe valves. 177–222. Rapheless valves. Scale bar 10 μm.

FIGURES 223–226. Achnanthidium epilithica sp. nov. SEM views of raphe valve. 223. External view of an entire raphe valve. 224. Internal view of an entire raphe valve. 225. Detail of the areolae on the external of the raphe valve. 226. Internal areola openings with fine hymenate structures. Scale bars 2 μm (223), 1 μm (224), 0.2 μm (225–226).

FIGURES 227–231. Achnanthidium epilithica sp. nov. SEM views of rapheless valve. 227. Girdle view, a frustule with convex rapheless valve. 228. External view of an entire rapheless valve. 229. Internal view of an entire rapheless valve. 230. Detail of the areolae on the external of the rapheless valve. 231. Internal areola openings with fine hymenate structures. Scale bars 2 μm (227–228), 1 μm (229), 0.2 μm (230–231).