Craticula australis Van de Vijver, Kopalová & Zidarova, 2015

Vijver, Bart Van De, Kopalová, Kateřina & Zidarova, Ralitsa, 2015, Three new Craticula species (Bacillariophyta) from the Maritime Antarctic Region, Phytotaxa 213 (1), pp. 35-45 : 36-37

Craticula australis Van de Vijver, Kopalová & Zidarova , sp. nov. ( Figs 1–9 )

LM ( Figs 1–7 ): valves broadly lanceolate with clearly convex margins gradually tapering towards the protracted, rostrate to weakly sub-capitate apices. Valve dimensions (n=10): length 18.0–19.5 μm, width 4.0–5.5 μm. Axial area very narrow, linear, forming a thickened, raised raphesternum. Central area absent. Raphe branches straight with weakly expanded proximal raphe endings. Distal raphe endings not discernible in LM. Striae almost parallel to very slightly radiate in the valve center, becoming slightly convergent ( Fig. 3 ), 24–28 in 10 μm, showing no difference in stria density throughout the valve. Areolae not visible in LM. SEM ( Figs 8–9 ): due to the rare nature of this taxon in the sample, SEM observations of the valve exterior were not possible. Only the valve interior could be examined. Striae uniseriate, composed (internally) of rounded to rectangular areolae. Areolae covered by perforated hymenes, located inside each areola ( Fig. 8 ). Striae near the central area weakly more distant than in the rest of the valve, occasionally with one shortened stria inserted within the normal striation pattern. Central nodule weakly raised. Internal proximal raphe endings positioned closely together, unilaterally shortly hooked ( Fig. 8 ). Distal raphe endings terminating on small helictoglossae ( Fig. 9 ).

Type:— JAMES ROSS ISLAND. Lachman 1: sample D2, 63° 47” 34.9’ S, 57° 48” 13.8’ W, L. Nedbalová, 22 January 2008 (holotype BR! slide no. 4392, isotype PLP! Slide no. 276, University of Antwerp, Belgium).

Ecology and Distribution: — Craticula australis was so far only observed in one sample, taken from the epilithon of a shallow coastal lake (Lachman 1) on Ulu Peninsula (James Ross Island). The lake was slightly alkaline (pH 7.6) with a rather high specific conductance value (>1000 μS/cm) and high total phosphorus (TP) and sulphate levels (592 μg/l and 162 mg /l respectively). The sample was dominated by Nitzschia homburgiensis Lange-Bert. (1978: 650–651) and Humidophila australis (Van de Vijver & Sabbe in Van de Vijver et al. 2010: 438) Lowe et al. (2014: 357).

Etymology:— The specific epithet refers to the distribution the taxon in the southern hemisphere (Latin: australis = southern).

Figures

FIGURES 1–9. Craticula australis. LM & SEM pictures taken from the holotype population (sample D02) from Lachman Lake I, James Ross Island. 1–7. Light microscopy observations. 8. Internal view of the central area with focus on the proximal raphe endings and the perforated areola occlusions. 9. Internal view of an entire valve showing the raphe and the variable distance between the striae. Scale bar represents 10 μm except for Fig. 8 where scale bar = 1 μm.