Planothidium wetzelectorianum Kopalová, Zidarova & Van de Vijver sp. nov.

Figs 25–57

Etymology

The species is named after our dear friends and colleagues Dr. Carlos Wetzel and Prof. Luc Ector [Luxembourg Institute of Science and Technology (LIST)] in recognition of the long and fruitful collaboration we had (and have) with these two excellent diatom scientists.

Type

Monolith Lake, James Ross Island, Antarctica, sample JRI-011 (63°53′52.3″S 57°57′29.0″W) (leg. L. Nedbalová), coll. date: 1 Feb. 2008 (holo-: slide no. BR–4437; iso-: slide PLP–293, University of Antwerp, Belgium).

Description

Light microscopy (Figs 25–52)

Frustules in girdle view nearly straight to weakly curved (Fig. 25). Valves linear-elliptical becoming elliptical in smaller specimens. Valve margins convex with broadly rounded, never protracted apices. Neither cavum nor sinus present. Valve dimensions (n = 25): length 5.5–10.0 µm, width 2.6–3.2 µm. Raphe valve (Figs 26–38): axial area very narrow. Central area absent or weakly enlarged due to shortening of two central striae. Raphe straight, difficult to see in LM. Proximal raphe endings indistinct, straight. Distal endings not discernible. Transapical striae weakly radiate throughout the entire valve, clearly broader than the virgae, 14–15 in 10 µm. Areolae not discernible. Rapheless valve (Figs 39–52): axial area very narrow, linear. Central area asymmetrically enlarged due to shortening of one central stria, never forming fascia. Striae radiate throughout, more radiate near the apices, as broad as or broader than the virgae, 16–18 in 10 µm.

Scanning electron microscopy (Figs 53–57)

Raphe valve (Figs 53–55): raphe branches almost straight terminating in indistinct straight pores (Fig. 53). Distal fissures absent (Fig. 54). Raphe terminating immediately beyond the last stria (Fig. 54). Striae composed of 3–5 rows of small, rounded areolae (Figs 53, 54). Near the axial area, each stria composed of usually 4–5 rows of areolae, towards the valve margin only 3 rows of areolae present in the stria (Fig. 54). Virgae clearly narrower than the striae (Fig. 53). Striae only shortly continuing onto the mantle (Fig. 53). Internally areolae covered by star-shaped hymenes (Fig. 55). Virgae clearly thickened and raised. Proximal raphe endings short, deflected (Fig. 55). Distal endings terminating onto small helictoglossae (Fig. 55). Rapheless valve (Figs 56–57): axial area weakly lanceolate. Striae always composed of 3 rows of small, rounded areolae (Fig. 56). Towards the axial area, striae becoming narrower (Fig. 56). Virgae usually as broad or slightly narrower than the striae (Fig. 56). Asymmetric central area clearly observable. Internally areolae covered by hymenes (Fig. 57). Virgae clearly thickened (Fig. 57).

Ecology and distribution

Planothidium wetzelectorianum sp. nov. was only found on James Ross Island in the epilithon and epipelon of Monolith Lake on the Ulu Peninsula. This relatively large lake has an almost circumneutral pH (7.2), a rather lower conductivity value (120 µS/cm) and low nutrient and sulphate values. The samples are dominated by several taxa from the N. perminuta complex [N. kleinteichiana Hamsher et al. (Hamsher et al. in press), N. velazqueziana Hamsher et al. (Hamsher et al. in press) and N. annewillemsiana Hamsher et al. (Hamsher et al. in press)], Humidophila australis (Van de Vijver & Sabbe) Lowe et al. (Lowe et al. 2014) and Achnanthidium australexiguum Van de Vijver in Taylor et al. (2014).