Psammothidium confusoneglectum Kopalova, Zidarova & Van de Vijver 2016, sp. nov.

Psammothidium confusoneglectum Kopalová, Zidarova & Van de Vijver sp. nov.

Figs 58–85

The specific epithet refers to the possible confusion with Psammothidium confusum (Manguin) Van de Vijver.

Byers Peninsula, Livingston Island, South Shetland Islands, Antarctica, sample BYM-051 (62°38′20.1″S 61°06′44.2″W) (leg. B. Van de Vijver), coll. date: 15 Jan. 2009 (holo-: slide no. BR–4438; iso-: slide PLP–294, University of Antwerp, Belgium).

Light microscopy (Figs 58–82)

Valves broadly elliptic-lanceolate with clearly convex margins gradually tapering towards the broadly rounded, non-protracted apices. Valve dimensions (n = 30): length 9–12 µm, width 3.8–4.5 µm. Raphe valve (Figs 58–70): axial area narrow, linear, not widening towards central area. Central area forming a rectangular to bow-tie-shaped fascia with occasionally one to several shortened striae near the valve margins (Figs 62–64, 68). Raphe straight with almost indistinct, straight proximal endings. Distal fissures not discernible in LM. Transapical striae weakly radiate near the central area, becoming more radiate towards the apices, 30–34 in 10 µm. Areolae not discernible in LM. Rapheless valve (Figs 71–82): axial area very narrow, linear distinctly widening towards the central area. Central area rounded to apically elliptical, bow-tie shaped widening towards the valve margins, almost forming a fascia. Regularly, shortened striae present near the valve margins. Transapical striae weakly radiate throughout becoming more radiate towards the apices, 33–36 in 10 µm.

Scanning electron microscopy (Figs 83–85)

Raphe valve (Fig. 83): striae uniseriate, composed of small, rounded to rectangular areolae, the largest areolae located close to the axial area. Number of areolae per stria diminishing towards the axial area. Near valve margins, last areola transapically elongated, slit-like. A row of slit-like areolae present on the mantle. Raphe branches almost straight. Proximal raphe endings straight, drop-like expanded (Fig. 83). Distal endings short, weakly drop-like expanded. Rapheless valve (Figs 84–85): central area slightly depressed, forming a weak pseudoraphe (Fig. 84). Striae uniseriate composed of small, rounded to rectangular and transapically elongated areolae (Fig. 84). Slit-like areolae present near the valve margins and onto the mantle (Fig. 84). In the central area, several slit-like areolae visible near the valve margin. Internally areolae transapically elongated, covered by individual perforated hymenes (Fig. 85). Virgae slightly raised. Small silica bars separating the areolae (Fig. 85).

This new species was up to now only observed on Livingston Island. The largest population was found living in mosses submerged in a large lake showing a circumneutral pH (7.3) and a low conductivity level (<100 µS/cm). The sample was dominated by several Psammothidium taxa such as P. subatomoides (Hust.) Bukht. & Round (Bukhtiyarova & Round 1996), P. abundans (Manguin) Bukht. & Round (Bukhtiyarova & Round 1996) and P. papilio (D.E.Kellogg, Stuiver, T.B.Kellogg & Denton) Kopalová & Van de Vijver in Kopalová et al. (2012).