Brachysira conamarae Kennedy & Allott, 2017

Kennedy, Bryan & Allott, Norman, 2017, A review of the genus Brachysira in Ireland with the description of Brachysira praegeri and Brachysira conamarae, new raphid diatoms (Bacillariophyceae) from high status waterbodies, Phytotaxa 326 (1), pp. 1-27 : 10-12

Brachysira conamarae Kennedy & Allott , sp. nov. ( Figs 25–33 )

Type:— IRELAND. Co. Galway: Lough Maumwee , degrees 53.47439656N, 9.54091316W, elev. 44.3 m, coll. B. Kennedy, coll. date 19 April 2007. (Holotype: specimen here designated Finder: L 60N2 (The England FinderTM Graticule) TCD0018138 , Holotype illustrated in Fig. 25 ; type, sample ZU 10/79, Hustedt Collection, Alfred Wegener Institute) .

LM & SEM ( Figs 25–33 ):—Cells solitary.Valves lanceolate, tapering uniformly to weakly or hardly protracted rounded apices. Valve dimensions (n=15): length 23–40.0 μm, width 5–6 μm. Axial area narrow linear, sometimes appearing more prominent ( Figs 26–27 ). Central area indistinctly lanceolate and only slightly wider than axial area. Valve face flat, surrounded by an elevated ridge, thickened near valve apices ( Figs 28–30, 33 ). Raphe straight, filiform with simple, straight, slightly punctiform proximal raphe endings. Distal raphe endings T –shaped with straight branches. Raphe branches bordered by a thickening of the axial area, lacking clear ribs, only slightly more prominent towards apices ( Figs 28–30 ). Striae lineate, uniseriate, radiate at center parallel to weakly convergent at apices, 34–37 in 10 μm. Striae composed of 2–3 transapically elongated areolae, similar or dissimilar in length, decreasing in number both at valve centre and apices. A single elongate areola per stria occasionally at valve centre. Voigt discontinuity not observed. Irregular gaps present between areolae producing discontinuous apically running hyaline undulations, especially prominent towards mid-valve. Small narrowly pointed papillae present on interstriae, usually 4–5 per interstriae at valve centre, reducing to a single papilla at apices. Papillae occasionally irregularly dispersed over central or axial area along full length of raphe and in close proximity to it ( Figs 27–32 ). Single elongate bacilliform areola, lacking papillae on mantle. Areolae foramina with small indentations. Around apices, mantle striae close together ( Figs 28–30 ).

Etymology:—The specific epithet refers to the original Irish spelling (Conamara) of Connemara, a mountainous region in Co. Galway in western Ireland where the species was discovered.

Similar species:—The comparable size and stria density of larger valves of the B. microcephala morphotype reported here (BMIC-2; Figs 173–205 ) makes it difficult to separate B. conamarae with LM alone. An absence of siliceous ribs bordering the raphe is the principal ultrastructural characteristic separating it from this closely related taxon and is only discernible with SEM. The range in stria density overlaps with BMIC-2. Conspecificity with B. procera can be ruled out based on a coarser stria density (27–30 vs. 34–37 10 μm in B. conamarae ). B. garrensis also has significantly reduced ribs bordering the raphe relative to other Brachysira , but the valves of B. conamarae are much larger and possess abundant papillae between the coarser striae which are lacking in the former species. B. guarrerai Vouilloud et al. (2014: 152) notably possesses only a single prominent rib with omission of the rib at the junction between the valve face and mantle. It also lacks papillae and has a more protracted outline. The absence of transapical ribs bordering the raphe is a feature of the morphology of Brachysira lecohui Lange-Bertalot (in Lange-Bertalot & Moser 1994: 39) but stria density is lower and a lack of papillae and other features of its ultrastructure prevent confusion with this taxon. Wang & Wu (2005) provide an SEM micrograph for the heteropolar Brachysira steindorfiana Moser, Lange-Bertalot & Metzeltin (1998: 101) with a similar absence of silica ribs bordering the raphe, but the morphology of this taxon does not otherwise resemble B. conamarae . While the presence of conspicuous papillae along the axial area has been observed for other taxa (e.g. B. australofollis , B. julio and B. nubigena in Lange-Bertalot & Moser 1994: 17, 37, 54) they were also occasionally absent in B. conamarae . A difference in the valve outline and denser striae easily separates it from these species.

Distribution & Ecology:— Brachysira conamarae has been found so far as occasional valves in two lakes in

Connemara, Co. Galway. It co-occurs with B. praegeri and is associated with the same diatom flora as this species. It occurs in near-pristine waters of low alkalinity which are slightly acidic (alkalinity=5.0 mg/l CaCO 3, mean pH=6.8, min. pH=6.4) and low colour (Hazen=29) with nutrients below the limit of detection.

Figures

FIGURES 25–33. Brachysira conamarae sp. nov. Figs 25–26. LM. Fig. 25. Holotype specimen (TCD0018138). Figs 27–33. SEM. Fig. 27. External view of an elongate valve with slightly more prominent axial area. Figs 28–30. Variation in valve morphology apparent for the holotype population with varying pattern of occurrence of papillae over the valve face. Fig. 31. Oblique valve in tilt illustrating ultrastructural features. Fig. 32. Detail of the centre of the frustule with papillae over the entire valve face. Fig. 33. Detail of the valve end and T-shape distal raphe endings. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 173–205. Brachysira microcephala morphotype BMIC-2. Figs 173–197. LM. Figs. 198–205. SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.