Mastogloia seychellensis Grunow, 1878

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

Mastogloia seychellensis Grunow Figs 80–82

Section Paradoxae

Ref. illus.: Hustedt 1931 –1959, fig. 958; Loir & Novarino 2013, pl. 21c

Samples: GU52Q-10a

Dimensions: Length 45–48 µm, width 13 µm; transapical striae 27 in 10 µm, longitudinal striae 26 in 10 µm.

Diagnostics: Elliptical-lanceolate valves with rostrate apices, the partecta strongly displaced toward the midline and with evident ducts leading obliquely to the valvocopula wall.

Comments: M. seychellensis is similar to M. paradoxa Grunow ( Hustedt 1931 –1959, fig. 953; in our flora: Lobban et al. 2012, pl. 34, figs 3–5) and M. similis Hustedt ( Hustedt 1931 –1959, fig. 954); the latter differs from M. paradoxa only in having a straight raphe. In these taxa the middle chambers are distinctly larger than the rest, instead of forming a graded series as in M. seychellensis , and both have axial costae along the raphe, which are absent from M. seychellensis . The size ranges of M. seychellensis and M. paradoxa are respectively 30–50 µm and 50–60 µm according to Hustedt. Although Hustedt showed the raphe of M. seychellensis as perfectly straight, the Guam specimens have a distinctly wavy raphe. On the strength of the difference Hustedt (1931 –1959) used to erect M. similis , this would be enough to exclude these specimens from M. seychellensis but we do not yet have adequate material to address the differences among these species.

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.