Figs 86–109
The specific epithet refers to the similarity with P. papilio and the larger valve dimensions.
Byers Peninsula, Livingston Island, South Shetland Islands, Antarctica, sample BYM-008 ( 62°40′11.3″S 61°08′45.3″W) (leg. B. Van de Vijver), coll. date: 9 Jan. 2009 (holo-: slide no. BR–4439; iso-: slide PLP–295, University of Antwerp, Belgium).
Light microscopy ( Figs 86–105)
Valves lanceolate to lanceolate-elliptic with convex to sometimes more straight margins gradually tapering towards the broad cuneately rounded apices. Valve dimensions (n = 40): length 15–20 µm, width 4.5–5.5 µm. Raphe valve ( Figs 96–105): valves clearly convex. Axial area narrow, linear, almost not widening towards the central area. Central area forming a broad rectangular to bow-tieshaped subfascia with several (3–5) shortened striae present near the valve margins. Raphe straight with indistinct, straight proximal endings. Distal fissures not discernible in LM. Transapical striae weakly radiate near the central area, becoming more strongly radiate towards the apices, 28–30 in 10 µm. Areolae not discernible in LM. Rapheless valve ( Figs 86–95): thickened marginal crest clearly visible in LM. Axial area very narrow, linear-lanceolate, clearly widening towards the central area. Pseudoraphe clearly present as a series of irregular depressions in the axial area. Central area rounded to rhombical, bordered by several shortened striae. Fascia never present. Transapical striae weakly radiate throughout becoming more strongly radiate towards the apices, 26–29 in 10 µm.
Scanning electron microscopy ( Figs 106–109)
Raphe valve ( Figs 106–107): axial area weakly raised and more heavily silicified ( Fig. 106). Striae uniseriate, composed of long series of very small, rounded to rectangular areolae ( Fig. 106). Number of areolae per striae diminishing towards the axial area ( Fig. 106). On the valve face/margin junction, one transapically elongated areola present. Raphe branches almost straight ( Fig. 106). Proximal raphe endings straight, simple, never expanded ( Fig. 106). Distal endings short, terminating near the last striae at the apices ( Fig. 106). Internally, areolae rectangular, covered by perforated hymenes ( Fig. 107). Proximal raphe endings bent into opposite directions. Distal endings terminating onto small helictoglossae ( Fig. 107). Rapheless valve ( Figs 108–109): Valve clearly concave. Thin, raised marginal crest bordering the entire valve. Axial area with irregular depressions, forming a clear pseudoraphe ( Fig. 108). Striae uniseriate composed of small, rounded areolae. Internally areolae covered by individual perforated hymenes ( Fig. 109). Virgae not raised.
This new species was up to now only observed with certainty on Livingston Island. The largest population was found living in a terrestrial moss vegetation, at the edge of a shallow lake. The sampling site was clearly influenced by animals with remains of penguins present on the mosses. The sample was dominated by several Psammothidium taxa such as P. germainii (Manguin) Sabbe ( Sabbe et al. 2003), P. aretasii (Manguin) Le Cohu ( Le Cohu 2005) and P. incognitum (Krasske) Van de Vijver & Beyens ( Van de Vijver et al. 2002).