Craticula petradeblockiana 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 : 41

Craticula petradeblockiana Van de Vijver, Kopalová & Zidarova , sp. nov. ( Figs 21–35 )

LM ( Figs 21–31 ): valves elliptical with clearly convex margins and shortly protracted, rostrate apices, set on well-developed shoulders. Valve dimension (n=40): length 20–22 μm, width 6.0–7.5 μm. Axial area narrow to moderately broad, linear to linear-lanceolate, weakly widened near the central area. Central area almost absent, only visible due to the widening of the axial area, and occasionally shortened striae inserted into the normal striation pattern ( Figs 25, 30 ). Raphe branches straight, filiform with simple, weakly expanded proximal raphe endings and hooked distal endings ( Figs 26, 27 ). Striae weakly radiate near the central area becoming parallel to slightly convergent near the apices, 20–22 in 10 μm. Near the central area, striae more distantly spaced contrary to the apices where striae more closely together positioned. Areolae not discernible in LM. SEM ( Figs 32–35 ): striae externally composed of apically elongated, rectangular to rounded (bordering the axial area) areolae ( Fig. 32 ). External proximal raphe endings droplike, straight ( Fig. 32 ). Distal fissures hooked, slightly extending onto the valve mantle. Internally, central nodule very weakly raised ( Figs 34, 35 ). Internal proximal raphe endings relatively distant, straight to very slightly unilaterally shortly bent ( Figs 34, 35 ). Distal raphe endings terminating on small helictoglossae (Fig. 36). Areolae covered by perforated hymenes, located inside each areola ( Figs 33 , 37).

Type:— JAMES ROSS ISLAND. Ulu Peninsula: Water-supply Creek, sample Vo4, 63° 48” 58.2’ S, 57° 54” 55.1 W, J. Elster, 01 February 2006 (holotype BR! slide no. 4394, isotype PLP! Slide no. 278, University of Antwerp, Belgium).

Ecology and Distribution: — Craticula petradeblockiana was found in a sample, collected from Water-Supply Creek, on Ulu Peninsula at 2.2 km from the ocean at an altitude of 39 m a.s.l. Unfortunately, more ecological information was not collected when sampling. On the nearby Livingston Island (South Shetland Islands), C. petradeblockiana has been rarely observed in samples taken from streams and ponds, though more valves were found only in a pond with turbid water, having a relatively low conductance (212 μS/cm) and NO 3 -- N (0.4 mg /l) and PO 4 3-- P (0.21 mg /l) concentrations (Zidarova, pers. obvs.) In all cases the samples were dominated by various Mayamaea and Fistulifera taxa.

Etymology: — The species is named after our dear colleague, Dr. Petra De Block (Botanic Garden Meise, Belgium) in recognition of her taxonomic work, mainly on the angiosperm Rubiaceae family from Madagascar.

Figures

FIGURES 21–35. Craticula petradeblockiana. LM & SEM pictures taken from the holotype population (sample Vo4) from Water-Supply Creek, James Ross Island.21–31. Light microscopy observations. 32. External view on an entire valve showing the raphe and the variation in stria distance in the central area compared to the rest of the valve. 33. External detail of the perforated areola occlusions in the areolar canal. 34. Internal view of an entire valve showing the raphe. 35. Internal detail of the central area. 36. Internal detail of a valve apex showing the small helictoglossa. 37. Internal detail of the areolae showing the position of the hymenes. Scale bar represents 10 μm except for Figs 33, 36 & 37 where scale bar = 1 μm and Fig. 35 where scale bar = 5 μm.