Entomoneis sinensis Bing Liu & D.M. Williams sp. nov.

Figs 1, 2, 3, 4, 5, 6, 7, 14

Holotype.

Slide BM 81941, the holotype specimen circled on the slide, illustrated here as Fig. 1A; isotype, slide JIU202101, illustrated here as Fig. 1B.

Type locality.

China. Qinghai Province, Lake Qinghai, a sampling point near the lakeshore, 36°50'34" N, 99°42'39" E, 3210 m a.s.l., collected by Bing Liu, 19 July 2019.

Description.

LM (Fig. 1). Frustule panduriform in girdle view (Fig. 1A-F). Frustule dimensions (n = 41): length 22.6-42.6 μm, width 8.9-14.1 μm at its centre, 14.6-19.8 μm at its widest region. Two distinct 8-shaped loops are present in each frustule (indicated in Fig. 1D-F), one 8-shaped loop evident in each valve (Fig. 1G-O). Simple, arcuate junction line discernible in some specimens (indicated in Fig. 1H and I). Costae and striae invisible under LM. Girdle bands numerous.

SEM, girdle view (Figs 2 - 4). Frustule panduriform with low keel (Fig. 2A and B; Fig. 3A-F, indicated by fused part). Cells having a 5:2 configuration of girdle bands, i.e. five girdle bands associated with the epivalve and two associated with the hypovalve (Fig. 2C-F, labelled in Fig. 2C and D). Junction line simple, arcuate (Fig. 3A). Two sides of the keel fused so that subraphe canal connects the cell lumen only near the central ending (Fig. 3B and C, arrow, respectively; see also Fig. 7B, arrow) and distal raphe ending (Fig. 3D, arrow). Short bar-like basal fibulae forming junction line (Fig. 3E and F, three arrows, respectively). Each pars media of valvocopula forming 8-shaped loop that is very distinct under LM (Fig. 4A-D). Each costa extending from raphe canal to inconspicuous mantle, warts bearing on each costa (Fig. 4E). Structure of each girdle bands similar, composed of pars exterior, pars media and pars interior (Fig. 4E). Pars media like a sternum, not located at the mid-line but slightly displaced towards pars interior (Fig. 4G). Both pars exterior and interior composed of one row of elongate poroids and each elongate poroid consisting of two costae and a hymen strip between them (thus the elongate poroid is n-shaped), with the n-shaped poroid of pars exterior longer than that of pars interior (Fig. 4F and G).

SEM, valve view (Figs 5 - 7). Valve linear-lanceolate, keel Ƨ-shaped (Fig. 5A, Fig. 6A-C). Costae mostly running from raphe canal to mantle (Fig. 5B), but some bifurcate (Fig. 5B, arrow), some terminating halfway to mantle (Fig. 5C, short costae). Each stria included between two adjacent costae, composed of one hymen strip (Fig. 5A-F). This type of hymen strip belonging to Type Two hymen strip, which is a siliceous membrane strip perforated by two rows of elongate (linear) pores next to the transapical costae and two rows of rounded pores between these two rows of linear pores (Fig. 14A and B). Mantle inconspicuous (Fig. 5B). Two total rows of separated areolae present along the raphe on both sides of the keel (Fig. 5B, four wavy arrows), but do not extend to the apex (Fig. 5E and F, six arrows, respectively). The hymenes occluding these separated areolae have the same structure as the hymen strip on striae (Fig. 5F, arrows). Stria density 36-43 in 10 μm (n = 7). Two proximal raphe endings slightly dilated and a pore-like structure located at the centre of central nodule (Fig. 6D-F, arrow, respectively). Internally, one cell bearing only one lumen, no sub-compartment present (Fig. 7).

Etymology.

Named after China where the species was found (the specific locality is Lake Qinghai).

Ecology and distribution.

Entomoneis sinensis was found on the stone surfaces in Lake Qinghai. The following environmental parameters were measured in the field. Conductivity was 16296.7 ± 86.2 μS /cm, pH was 9.14 ± 0.01 and water temperature was 15.5 ± 0.3°C. According to above data and because Lake Qinghai is a brackish water lake, Entomoneis sinensis should be a brackish water diatom species. So far, E. sinensis is only found in the type locality and is a dominant species.