Achnanthidium caledonicum (Lange-Bert.) Lange-Bert., 1999

Jüttner, Ingrid, Hamilton, Paul B., Wetzel, Carlos E., De, Bart Van, Vijver, King, Lydia, Kelly, Martyn G., Williams, David M. & Ector, Luc, 2022, A study of the morphology and distribution of four Achnanthidium Kütz. species (Bacillariophyta), implications for ecological status assessment, and description of two new European species, Cryptogamie, Algologie 20 (10), pp. 147-176 : 152-153

Achnanthidium caledonicum (Lange-Bert.) Lange-Bert.

( Figs 2-4 )

Iconographia Diatomologica 6: 270-283 (Lange-Bertalot 1999). — Achnanthes microcephala f. scotica J.R.Carter in Carter & Bailey- Watts, Nova Hedwigia 33: 534, pl. 1, fig. 31 (Carter & Bailey-Watts 1981). — Achnanthes minutissima var. scotica (J.R.Carter) Lange- Bert.in Lange-Bertalot & Krammer, Bibliotheca Diatomologica 18: 106, pl. 55, figs 4-12, pl. 57, fig. 11, pl. 67, figs 35-56 (Lange-Bertalot & Krammer 1989). — Achnanthes scotica (J.R.Carter) Lange-Bert., Bibliotheca Diatomologica 27: 8 (Lange-Bertalot 1993), nom. illeg., non Achnanthes scotica Flower & V.J.Jones, Diatom Research 4: 228, figs 1-7, 42-53 ( Flower & Jones 1989). — Achnanthidium minutissimum var. scoticum (J.R.Carter) H.Cremer in Cremer & Wagner, Polar Biology 26: 108 ( Cremer & Wagner 2003). — Basionym: Achnanthes caledonica Lange-Bert. in Lange-Bertalot & Moser, Bibliotheca Diatomologica 29: 95 (Lange-Bertalot & Moser 1994).

DESCRIPTION

LM ( Fig. 2 A-AN)

Frustules moderately arched, with convex rapheless valves, concave raphe valves, and recurved poles. Valves linear with large, subcapitate to capitate poles, the latter sometimes wider than the maximum valve width at valve centre. Valve margins tapering slightly towards a small constriction before poles. At valve centre, margins slightly inflated, sometimes unilaterally, or straight. Valve dimensions (n = 20): length 17.5-37.5 µm, width at valve centre: 3.0-3.5 µm. On raphe valve (RV), shape of central area variable, either a small transverse fascia, or oval to round, bordered by one or several slightly shortened striae. Raphe filiform, straight, central pores hardly widened, distantly placed at margin of central area. Central area on rapheless valve (RL) narrow lanceolate. Axial area narrow linear on both valves. Striae radiate throughout on both valves, more distantly placed in valve centre, 30-32 in 10 µm.

SEM ( Figs 3 A-F; 4A-D)

Raphe located on slightly raised sternum, terminal fissures straight terminating at valve/mantle junction. Internally, central raphe endings shortly deflected to opposite sides, terminal raphe endings form small helictoglossae. Striae composed of 2-4 (RV) and 2-5 (RL) areolae. Areolae round or oval, areolae adjacent to valve margin slit-like. Row of transapically elongated areolae on mantle separated from areolae on valve face by hyaline area.

On the type slide (lecto-, BM[BM 94890], ex J.R. Carter 3665), the species is common, but many specimens are positioned in girdle view. The central area is often a fascia, as mentioned by Carter (Carter & Bailey-Watts 1981), but sometimes less conspicuous, irregular, and formed by more widely spaced central striae.

Figures

FIG. 2. — A-H, Achnanthes microcephala f. scotica J.R.Carter,type from Ardislaigh Lochan,Scotland;I-AN, Achnanthidium caledonicum (Lange-Bert.) Lange-Bert.; I-S, specimens from Lochan na Ba Ruaidhe, West Sutherland, Scotland; T-Y, specimens from Vilsalpsee, Austria; Z-AG, specimens from Brunnsee, Germany; AH-AN, specimens from Plansee, Austria; A-F, K-X, AA-AN, LM views of valves; G-J, Y, Z, LM views of frustules in girdle view. Scale bar: 10 µm.

FIG. 3. — Achnanthidium caledonicum (Lange-Bert.) Lange-Bert.:A-B, specimens from Brunnsee,Germany; C-F, specimens from Scotland,2012,44sto;A, SEM external view of whole raphe valve and rapheless valve; B, SEM external view of whole raphe valve, mantle and girdle bands at pole; C, SEM external view of valve centre of raphe valve; D, SEM external view of valve centre of rapheless valve; E, SEM external view of pole of raphe valve; F, SEM external view of pole of rapheless valve. Scale bars: A, 10 µm; B, 5 µm; C-F, 3 µm.

FIG. 4. — Achnanthidium caledonicum (Lange-Bert.) Lange-Bert.:A, C, specimens from Brunnsee,Germany;B, D, specimens from Scotland,2012,44sto; A, SEM external view of frustule in girdle view and valve face of rapheless valve; B, SEM external view of pole in girdle view and valve mantle; C, SEM internal view of whole raphe valve; D, SEM internal view of valve centre of raphe valve. Scale bars: A, 10 µm; B, D, 3 µm; C, 5 µm.