Nitzschia williamsii Alakananda, P.B.Hamilton & Karthick, 2012

Alakananda, B., Mahesh, M. K., Hamilton, Paul B., Supriya, G., Karthick, B. & Ramachandra, T. V., 2012, Two new species of Nitzschia (Bacillariophyta) from shallow wetlands of Peninsular India, Phytotaxa 54 (1), pp. 13-25 : 19

Nitzschia williamsii Alakananda, P.B.Hamilton & Karthick , sp. nov. ( Figs 27–53)

Valves spindle-formed with flatly-rounded apices. Frustules twisted typically, showing valves tilted, with both valve and mantle exposed ( Figs 45–48 ). Length 42–62 µm, width 2.5–5 µm with 12–14 fibulae, 28–35 striae and ~50 areolae in 10 µm. Keel elevated and marginal from valve face in centre ( Fig. 45 ). Raphe continuous, positioned next to a thickened ridge atop keel. Terminal raphe fissures form a small hook along each apex mantle ( Figs 47, 48 ). Striae uniseriate and recessed between elevated ridges on valve face ( Fig. 49 ). Keel with single series of areolae on either side of raphe. Keel and valve face areolae round, occluded by recessed hymen (poroid plate) ( Fig. 50 ). Internally, areolae are irregularly spaced and not apically aligned ( Fig. 52 ). Areolae rounded and covered by hymen. Fibulae round to rectangular, weakly expanding to form attachments on internal valve face and mantle ( Figs 51, 52 ). The two central fibulae are separated by a space equivalent to one to two times their respective widths which corresponds to the presence of a central area; close to apices fibulae broader and more flattened, with small interfibular spaces which are less than width of a single fibula ( Fig. 53 ). Copulae narrow open bands with a single row of pores on pars exterior.

Type:— INDIA. Bangalore : Thalghattapura Wetland at Bangalore, 12° 52' 1" N, 77° 31' 52.66" E, elevation 900 m, March 2009. B.Alakananda & G.Supriya s.n. (holotype CESH-05-1882! (circled specimen on slide) isotype CANA 85056 ! (circled specimen on slide))

Ecology:— Nitzschia williamsii was found to be abundant in wetlands with alkaline waters, basic pH (8.7 ± 0.3), alkalinity of 228 ± 91.9 mgL -1, 0.05 ± 0.01 mgL -1 nitrates and 0.05 ± 0.003 mgL -1 phosphates. Moderate specific conductance (789.5 ± 1.4 µScm -1), and oxygen demand (BOD, 13 ± 0.4 mgL -1; COD, 32 ± 2.8 mgL -1) concentrations were recorded. This wetland catchment was characterized by more open spaces and less built-up areas compared to other wetlands in the region. The autecology of associated taxa needs to be further defined.

Etymology:— The species epithet is named for our colleague and friend Dr. David M. Williams (Natural History Museum, London) whose support for diatom studies in India is hereby acknowledged.

Observations:— There are many taxa in the subgenus Lanceolatae which have a linear-lanceolate attenuated to needle-like (aciculate) shaped valve ( Lange-Bertalot & Simonsen 1978). Differences between these are often subtle and mostly without SEM illustrations of the characters. Hustedt described a number of these taxa and in LM they are typically distinguished by a combination of characters from valve-shape to stria density ( Table 2). Nitzschia williamsii is distinguished by the linear attenuated (not strictly acicularis) shape, the rounded (not capitate) apices and stria density. Nitzschia williamsii is most similar to N. acicularioides Hustedt (1959: 415) , although the valves are more lanceolate, the striae are visible in LM and the fibulae are broader. Nitzschia subacicularis Hustedt (in Schmidt et al. 1922: pl. 348, fig. 76), N. suchlandti Hustedt (1943b: 233) and N. kuetzingioides Hustedt (1959: 417) are smaller with a more lanceolate valve outline and different stria densities, whereas N. rostellata Hustedt is strictly aciculoid with coarser striae. Nitzschia williamsii is easily distinguished from N. gracilis Hantzsch (in Cramer 1860 (7): 40) sensu lato by the much lower stria density. Nitzschia williamsii is often observed contorted especially towards the apices.

Figures

FIGURES 45–53. SEM micrographs of Nitzschia williamsii sp. nov. Fig. 45. SEM of external view of the entire valve. Fig. 46. SEM of internal view of the entire valve. Figs 47, 48. SEM of external view of the valve apex showing terminal raphe fissures form a small hook along each apex mantle. Figs 49, 50. SEM external view of uniseriate striae with areolae recessed between elevated ridges. Fig. 51. SEM of internal view of valve centre showing the uniseriate striae. Fig. 52. SEM of internal view of the valve showing the round to rectangular fibulae and its spacing. Fig. 53. SEM of internal view of the valve apex showing the internal terminal nodule. Scale bars in Figs 45, 46 = 10 µm; Figs 47, 48, 50, 53 = 2 µm; Fig. 49 = 0.5 µm; Figs 51, 52 = 1 µm. (Specimens from sample CANA 85056)