Luticola desmetii Kopalová & Van de Vijver, 2011

Kopalová, Kateŕina, Nedbalová, Linda, Haan, Myriam De & Vijver, Bart Van De, 2011, Description of five new species of the diatom genus Luticola (Bacillariophyta, Diadesmidaceae) found in lakes of James Ross Island (Maritime Antarctic Region), Phytotaxa 27, pp. 44-60 : 47-49

Luticola desmetii Kopalová & Van de Vijver , sp. nov. ( Figs 2–13 )

Valvae rhombicae at rhombicae-elloticae marginibus distincte convexis, apicibusque protractis, rostratis. Longitudo 22– 42.5 µm, latitudo 11.3–16.8 µm. Area axialis angustissima, paene linearis ad linearis-lanceolata, leviter dilatata in aream centralem. Sternum lineare adest marginatum depressionibus longitudinalibus. Area centralis irregularis, formans staurum rectangularem asymmetricum, marginatum serie una areolarum rotundatarum ad leviter transapicaliter elongatarum. Stigma solitaria magna rimiformis inter mediam partem valvae marginesque. Depressiones plures in area centrali, visibiles in microscopio photonico. Raphe filiformis, recta, terminationibus proximalibus indistinctis, fissurisque distalibus elongatis, deflexis. Striae transapicales radiatae in centro valvae, fortiter radiatae ad apices, 12–16 in 10 µm.

Type:— ANTARCTICA. James Ross Island , Ulu Peninsula, Blue-Green Lake, sample D51, leg. L. Nedbalová, coll. date 27/01/2009, slide no. BR-4241 (holotype BR, Fig. 7 is the encircled holotype specimen), slide PLP-189 (isotype University of Antwerp, Belgium), BRM-ZU8/06 (isotype BRM) .

Valves rhombic to rhombic-elliptical with inflated, distinctly convex margins ( Figs 2–8 ). Apices typically protracted, rostrate. Valve length 22–42.5 µm, valve width 11.3–16.8 µm (n=37). Axial area quite narrow, almost linear to linear-lanceolate, slightly widening towards the central area, formed by a raised, almost straight, linear sternum; bordered by longitudinal depressions ( Fig. 9 ). Central area irregular, forming a rectangular, asymmetrical stauros, bordered by one series of rounded to very weakly transapically elongated areolae. One large, slit-like isolated stigma present, located halfway between valve margin and valve centre ( Figs 9, 11 ). Multiple irregular, shallow depressions present in central area, visible in LM ( Figs 9, 11 ).

External raphe branches usually straight, with inconspicuous straight proximal raphe endings ( Figs 9, 11 ). Distal raphe endings elongated, deflected towards stigma-bearing side ( Figs 9, 12 ). Transapical striae radiate near valve centre, becoming strongly radiate towards poles, 12–16 in 10 µ m. Pattern of areolae rather irregular. Striae usually composed of 2–3 small, rounded areolae and one slit-like areola close to valve margin ( Fig. 9 ). Towards apices, striae composed of 1–2 strictly rounded areolae ( Fig. 12 ). Internally, poroids of valve face occluded by hymenes ( Figs 10, 13 ). Internal expression of stigma absent ( Fig. 13 ). Distinct stauros visible ( Fig. 13 ). Longitudinal canal covered by siliceous outgrowth ( Figs 10, 13 ). Internal proximal raphe endings terminate on edge of stauros ( Fig. 13 ). Distal raphe endings terminate on small helictoglossae ( Fig. 10 ).

Habitat, Ecology and Distribution:— To date, L. desmetii has been found only in one small kettle lake (Blue-Green Lake) on James Ross Island close to the Whisky Glacier. The largest population was found in an epilithon sample. The lake had a pH of 7.8, a low specific conductance (91 µS/cm) and was relatively species rich with 32 species observed, dominated by Nitzschia taxa belonging to the complex around Nitzschia perminuta (Grunow in Van Heurck 1881: pl.68. Fig. 31 ) Peragallo (1903: 672) and Psammothidium metakryophilum (Lange-Bertalot & Schmidt in Schmidt et al. 1990: 64) Sabbe (in Sabbe et al. 2003: 242). A record from the South Shetland Islands ( Håkansson & Jones 1994) has not be verified.

Etymology:— Luticola desmetii is named after our dear friend and colleague Prof. Dr. Willem De Smet (University of Antwerp, Belgium) in honour of his Arctic and Antarctic limnological work.

Observations: — At present, no Luticola taxa have a similar valve shape to L. desmetii . Luticola higleri and L. katkae Van de Vijver & Zidarova (in Van de Vijver, Zidarova & de Haan 2011: 143) have a similar irregular pattern of longitudinal depressions, raised sternum and shallow depressions in the axial and central area ( Van de Vijver et al. 2006, 2011). However, both taxa have a different valve outline with clearly capitate apices ( L. katkae ) and broadly rounded valves ( L. katkae and L. higleri ). Moreover, L. higleri shows a distinct marginal rim on the valve face/mantle margin, which is absent in L. desmetii . Both have short distal raphe fissures in contrast to the elongated, deflected distal raphe endings in L. desmetii . At present, no taxon of Luticola has a similar valve outline. Luticola heufleriana ( Grunow 1863: 155) D.G.Mann (in Round, Crawford & Mann 1990: 671) has weakly rhombic valves with clearly capitate apices, whereas L. lagerheimii ( Cleve 1894: Taf. 7:11) D.G.Mann (in Round, Crawford & Mann 1990: 671) has a comparable outline but forms long chains, has deflected proximal raphe endings and short marginal spines. Björck et al. (1996) reported L. heufleriana from sediment cores taken in three lakes on Ulu Peninsula, close to Blue-Green Lake. Although this record could not be verified, due to the lack of samples and illustrations, it is highly likely that this taxon should be attributed to L. desmetii .

Figures

FIGURES 2–13. Luticola desmetii Kopalová & Van de Vijver sp. nov. Light (LM) and scanning electron micrographs (SEM). Figs 2–8. Light microscopy images of type specimens from James Ross Island showing variation in size (Fig. 7 is the holotype). Fig. 9. SEM of external view of entire valve, showing raphe structure, position of stigma and striae structure. Fig. 10. SEM of internal view of entire valve, showing typical structure for species in the genus Luticola. Fig. 11. SEM of external detail view of central area for specimen in fig 9. Fig. 12. SEM of external detail of polar endings, showing deflected raphe for specimen in fig 9. Fig. 13. SEM of internal detail of the central area. LM scale bar = 10 µm; SEM scale bar = 1 µm except for Figs 9 & 10, where scale bar = 10 µm.

FIGURES 29–34. Luticola dolia Eposito & Spaulding. Light (LM) and scanning electron micrographs (SEM). Specimens from isotype slide INSTAAR 532. Figs 29–31. LM images. Fig. 32. SEM of external valve view. Fig. 33. SEM of external detail of raphe endings. Fig. 34. SEM of Internal valve view. LM scale bar = 10 µm. SEM scale bars = 10 µm except for Figs 33, where scale bars = 1 µm.