Nitzschia janischii Grunow, 1880

Lobban, Christopher S., 2015, Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis), Micronesica 2015 (2), pp. 1-49 : 9

Nitzschia janischii Grunow Figs 83–88

Ref. illus.: Grunow 1880, pl. 13, fig. 14; Peragallo & Peragallo 1897 –1908, pl. 76, fig. 14

Samples: GU44Z-15, GU44AK-2, GU44AR-2

Dimensions: Length 225–275 µm, width 7–9 µm; striae 23 in 10 µm; fibulae 4 in 10 µm Diagnostics: Extremely long valves with irregularly spaced fibulae extending completely across the valve face. Central nodule present ( Fig. 86 ). Areolae arranged in quincunx pattern of transapical and diagonal striae. Fourteen large, platelike plastids observed, with large pyrenoids ( Fig. 83 ).

Comments: N. janischii is most similar to Tryblionella scalaris (Ehrenberg) Siver & Hamilton [= N. scalaris (Ehrenberg) W. Smith ] (Ruck & Kociloek 2004, pl. 62–65), but that primarily freshwater/brackish species has ribs that extend only halfway across the valve face, besides the characters that make it Tryblionella . N. janischii was not recorded from The Bahamas ( Hein et al. 2008), Puerto Rico ( Hagelstein 1939, Navarro 1983b), Mahé ( Giffen 1980), or Tahiti ( Ricard 1977), and we are aware of no record other than Grunow’s. No ultrastructure images are cited in Gaul et al. (1993) or Henderson & Reimer (2003). Grunow (1880) illustrated only half of a specimen from the Hawaiian Islands, where it was “rare,” but Peragallo & Peragallo (1897 –1908) drew a whole valve; it is not clear whether they saw Grunow’s specimen, as they mention it only as a “curious exotic form,” perhaps not in the French flora. Grunow placed his species in Section Epithemioides , rather than Subgenus Denticula , but the differences are ill-defined. Denticula is now regarded as a separate genus, and Round et al. (1990, p. 622) commented that Denticula is, “Closely related to Nitzschia sect. Grunowia , from which it is difficult to separate, except on the extent of the fibulae.” In Denticula all the fibulae “extend across the valve face, forming partitions running from margin to margin. The fibulae widen at their bases (near the raphe) so that only small apertures (‘portulae’) are left connecting cell interior with subraphe canal.” This is also true of N. janischii , yet fibulae reaching the valve margin is not a synapomorphy for Denticula because a few other Nitzschia species also have this character, e.g., N. rhopalodioides Hustedt ( Hustedt 1955, p. 45, pl.15, fig. 16), and even N. ventricosa Kitton ( Lobban et al. 2012, pl. 61, figs 1, 2), although there, as in Gomphonitzschia clevei Grunow ( Grunow 1880, pl. 14, fig. 11, Peragallo & Peragallo 1897 –1908, pl. 76, fig. 15), some extend only part way and some costae extend part way back from the margin. At present there does not seem to be justification for reclassifying N. janischii in Denticula .

Figures

Figures 72–86. Fig. 72. Mastogloia pumila. Frustule showing two internal valve faces and valvocopulae; notice the variation in number of partecta (GU52P-1) (SEM). Figs 73–79. Mastogloia quinquecostata. Fig. 73. Live cell showing plastids (GU66A-5) (DIC). Figs 74–76. Frustule at three focal planes showing conopeum, areola pattern of valve face, and partecta (GU52Q-10a) (DIC). Figs 77, 78. Specimen at two focal planes showing the join in the conopeum (arrow) (GU44I-1) (DIC). Fig. 79. Oblique external view of valve showing seam along the conopeum (arrow) (GU66F-8) (SEM). Figs 80–82. Mastogloia seychellensis (GU52Q-10a). Figs 80, 81. Specimen at two focal planes, the valvocopula showing diagonal partectal ducts (DIC). Fig. 82. External view of valve (SEM). Figs 83–86. Nitzschia janischii. Fig. 83. Live cell in girdle view, showing nucleus (arrow) and plastids with pyrenoids (GU44AR-2) (DIC). Fig. 84. Portion of valve (GU44Z-15) (DIC). Figs 85, 86. Internal details of apex and central area, respectively, the latter showing the central nodule (arrow) (GU44AR-2) (SEM). Scale bars: Figs 73–78, 80–84 = 10 µm, Figs 72, 79, 85, 86 = 5 µm.

Figures 87–97. Figs 87, 88. Nitzschia janischii whole mount, details of central nodule and apex (GU44Z-15) (SEM). Figs 89–94. Nitzschia nienhuisii. Figs 89, 90. Girdle and valve views of the same cell in a wet mount (DIC). Figs 91, 92. Girdle and valve views of frustules in permanent mounts (GU44R-1, GU52P-1) (phase contrast). Figs 93, 94. Whole mount in SEM, and detail of central raphe endings (GU7R). Figs 95–97. Petroneis humerosa (GU44I-3). Fig. 95. Valve (DIC). Fig. 96. External view of valve (SEM). Fig. 97. Internal detail (SEM). Scale bars: Figs 87–93, 95, 96 = 10 µm, Fig. 94 = 2 µm, Fig. 97 = 5 µm.