Mastogloia quinquecostata Grunow

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 : 8-9

Mastogloia quinquecostata Grunow Figs 73–79

Section Sulcatae .

Ref. illus.: Peragallo & Peragallo 1897 –1908, pl. 6, fig. 3; Hustedt 1931 –1959, fig. 989; Ricard 1974, p. 3(21), fig. 7; Ricard 1975, figs 32–35; Paddock & Kemp 1990, fig. 20c; Witkowski et al. 2000, pl. 80, figs 7, 8

Samples: GU44I-2, GU44K-6, GU52Q-10a, GU66A-5, GU66F-8

Dimensions: Length 30–58 µm, width 14–19 µm; striae 22–24 in 10 µm

Diagnostics: Elliptical-lanceolate to rhombic-lanceolate valves with strong longitudinal lines and narrow partectal rings with square to apically rectangular partecta. Outer raphe is strongly sinuous and the inner straight; central endings straight.

Comments: The species name refers to the strong longitudinal lines, which mark the borders of the pseudoconopeum; a thin dark line marking the joint in the pseudoconopeum can sometimes be seen in LM and is clear in SEM ( Figs 77, 78 , arrows). Our stria densities are higher than those in Peragallo & Peragallo (1897 –1908) (15–16 in 10 µm) and Hustedt (1931 –1959) (16–20 in 10 µm). Montgomery (1978, pl. 138, figs A–E, pl. 139, figs C, D) has exterior SEMs labeled as M. quinquecostata , but they all show specimens with true conopea, open along the side, in contrast to Paddock & Kemp’s (1990) illustration. The partecta shown in Witkowski et al. (2000) do not match those in Hustedt’s (1931 –1956) drawings.

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.