Adlafia sinensis Bing Liu & D. M. Williams 2017, sp. nov.

LM: Valves lanceolate with rostrate to subcapitate apices (Figs 2–35), dimensions (n = 50): 11.0–17.0 μm long, 3.4– 4.2 μm broad.Axial area linear throughout valve’s entire length, central area almost non-existent (Figs 2–35). External central raphe endings discernible, opposite each other (e.g. Figs 27–35). Striae dense, uncountable.

SEM: Valves lanceolate with rostrate to subcapitate apices (Figs 36–38). Axial area linear gently widening at central area (Figs 36–38). Raphe with terminal fissures hooked towards secondary side; both fissures with slightly expanded central raphe endings bent towards primary side (Figs 36–38). Striae uniseriate, radiate, becoming abruptly convergent approaching apices, continuing onto mantle (e.g. Figs 41, 47–50). A few shortened striae present on each side of central valve (Figs 36–38). Stria density 32–36 (often 34) per 10 μm. Areolae round, occluded by hymenes outside (Figs 36–38). Internally, both proximal raphe endings deflected towards primary side of valve and distal raphe endings terminating in small helictoglossae (Fig. 39).

Frustule and girdle views: Frustules in girdle view rectangular composed of epivalve, hypovalve and valvocopula (Figs 40–42, EV, VC and HV respectively). Striae continuing onto deep mantle, c. 5–7 striae on mantle not continuous from valve (Fig. 41, arrowheads; Figs 47–50, arrows). Stria density on mantle 37–40 per 10 μm due to c. 5–7 striae more than valve face. Mantle becomes abruptly narrow close to apex where 4–6 rows of areolae merge into one row distal to terminal raphe fissures (Fig. 41, Fig. 43, curved arrow). Valvocopula connects epivalve and hypovalve (Figs 40–41, 43–46). Two rows of poroids on valvocopula (Fig. 38, arrow; Fig. 41, VC; Fig. 47, arrow), but in complete frustules, deep mantle covers one of two rows of valvocopula poroids located on pars interior of valvocopula, and only one row of poroids on pars exterior visible (Fig. 40, VC). Valvocopula composed of at least two parts that connect epivalve and hypovalve into a complete frustule; beneath the apices one part turns towards epivalve, the other turns towards hypovalve; both terminal ends of each part insert into the alternate part at inflection points of each (Figs 43–44, 46, arrows). Valvocopula open due to its two parts not being fused at inflection points (Figs 43–44, 46, arrows). Two segmental bands occur only beneath apices (Figs 44, B 2, B3).

Type: — CHINA. Hunan: Zhangjiajie National Forestry Park, the course of Jinbian brook, at Laomowang, 29°19’ 38” N, 110°26’32” E, 482 m a.s.l., Bing Liu, 29 th December 2015 , (holotype JIU! G201607 = Fig. 29; isotype BM! 101860 = Fig. 17).

Etymology: —Named after China, the country where the species was found.

Ecology:— The following environmental parameters were measured in the field. Conductivity was 102.7 ± 0.8 μS/cm, pH was 8.5 ± 0.7, and water temperature was 8.7 ± 0.2 °C. Since the diatom sample was scraped off the surfaces of stones and the water conductivity is near 100 μS/cm, Adlafia sinensis can be considered an epilithic diatom characteristic of moderate electrolyte content in freshwaters.