Achnanthidium maritimo-antarcticum Van de Vijver & Kopalová, 2014

Vijver, Bart Van De & Kopalová, Kateřina, 2014, Four Achnanthidium species (Bacillariophyta) formerly identified as Achnanthidium minutissimum from the Antarctic Region, European Journal of Taxonomy 79, pp. 1-19 : 6-8

Achnanthidium maritimo-antarcticum Van de Vijver & Kopalová sp. nov.

Figs 29-53

Morphological observations

Light microscopy ( Figs 29-49 )

Frustules in girdle view rectangular, bent around the transapical axis ( Figs 29, 30 ).Valves linear-lanceolate with parallel to slightly convex margins and clearly protracted, rostrate, occasionally subcapitate apices ( Figs 31-49 ). Valve dimensions (n=25): length 12–15 µm, width 2.3–2.7 µm. Raphe valve ( Figs 31-40 ) concave with a linear axial area, narrow to almost absent near the valve apices, hardly widening towards the central part of the valve. Central area irregular, formed by several more widely spaced striae. Raphe straight, filiform, invisible, with indistinct straight, simple proximal raphe endings. Distal raphe hardly discernible in LM. Striae slightly radiate throughout the entire valve, becoming more radiate and more densely spaced near the apices, 30– 33 in 10 µm, up to 40–42 in 10 µm near the valve apices. Rapheless valve ( Figs 41-49 ) slightly convex with very narrow, linear axial area, widening to form a weakly elliptically, never transapically elongated central area, never forming a fascia or subfascia. Central striae slightly more distantly spaced. Striae slightly radiate throughout, only slightly more denser near the apices, 30–32 in 10 µm.

Scanning electron microscopy ( Figs 50-53 )

Striae in the raphe valve composed of a series of 3 – 4 distinct, rounded to square areolae terminating in one transapically elongated, rectangular areola ( Fig. 50 ). Central striae composed of 2 rounded areolae and one transapically elongated areola near the valve margin ( Fig. 50 ). Occasionally, short slit-like areolae interposed between the central striae. Near the apices, striae only composed of 2–3 rounded areolae ( Fig. 50 ). Mantle areolae elongated, slit-like. Striae on the rapheless valve composed of 2–5 irregularly shaped (mostly rounded or elongated rectangular) areolae ( Fig. 51 ). Near the apices, striae showing lowest number of areolae ( Fig. 51 ). Internal areolae openings on both valves covered by hymenes ( Figs 52, 53 ). External raphe branches straight to weakly curved terminating in simple, short proximal and distal raphe endings ( Fig. 50 ). Distal raphe endings terminating just beyond the last apical stria ( Fig. 50 ). Internally, proximal raphe endings short, slightly bent. Distal raphe endings terminating in small helictoglossae ( Fig. 52 ).

Etymology

The specific epithet refers to the geographical area where the new species was found: Maritime Antarctic Region. The hyphen can and should be maintained in the species name based on art. 60.9 of the International Code of Nomenclature for algae, fungi and plants ( McNeill et al. 2012).

Type material

Holotype

Slide BR-4362 (National Botanic Garden, Meise, Belgium).

Type locality

Byers Peninsula , Livingston Island , South Shetland Islands, sample BY055 (62°37’41.7”S 61°06’30.4”W) ( Leg. B. Van de Vijver ; coll. date 15 Jan. 2009).

Isotypes

Slides PLP-252 ( UA, University of Antwerp, Belgium).

Ecology, distribution and associated diatom flora

The type population of A. maritimo-antarcticum was found in a large lake located on the central plateau of Byers Peninsula. The lake is characterized by a weakly alkaline pH (7.5) and a low conductivity (130 µS/cm). The ion composition in the lake is mainly dominated by Na + (20.0 mg/l) and Ca 2+ (12.1mg /l). Both nutrients (N-NO 3 +N-NO 2) and phosphate were rather low (25 µg /l and 10 µg /l resp.). The shoreline of the lake was completely covered with partly submerged mosses. Dominant taxa in the sample included Fragilaria capucina s.l. Desm. ( Desmazières 1825), Staurosirella sp., Navicula cremeri Van de Vijver & Zidarova in Van de Vijver et al. ( Van de Vijver et al. 2011d) and Nitzschia cf. perminuta. Smaller populations were found in other lakes such as Limnopolar Lake but these populations never exceed 1% of the total diatom composition. Due to force-fitting and taxonomic drift, the distribution of the new taxon in the Antarctic Region is unclear.

Figures

Figs 29-53. Achnanthidium maritimo-antarcticum Van de Vijver & Kopalová sp. nov. Light and scanning electron micrographs of the type population on Byers Peninsula (Livingston Island). 29-30. LM views of some frustules in girdle view. 31-40. LM views of raphe valves. 41-49. LM views of rapheless valves. 50. SEM external view of an entire raphe valve. 51. SEM external view of an entire rapheless valve. 52. SEM internal view of an entire raphe valve. 53. SEM internal view of an entire rapheless valve. Scale bars represent 10 µm.