Petroneis humerosa (Brébisson ex W. Smith) Stickle & D.G. Mann

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 : 10

Petroneis humerosa (Brébisson ex W. Smith) Stickle & D.G. Mann Figs 95–97

Ref. illus.: Peragallo & Peragallo 1897 –1908, pl. 27, fig. 20; Hustedt 1961 –1966, fig. 1702 (both as Navicula humerosa ); Witkowski et al. 2000, pl. 101, figs 2, 3, pl. 102, fig. 3

Samples: GU44I-3

Dimensions: Length 45–60 µm, width 29–34 µm; striae 12 in 10 µm

Diagnostics: Valves broad, linear, slightly rostrate. Strongly radiating striae with coarse areolae; short striae interspersed between longer ones along the central linear part of the valve.

Comments: Similar to P. latissima Gregory and P. monilifera Cleve ( Hustedt 1961 –1966, figs 1701, 1699), but those have coarser striae. There are a number of small ultrastructural differences between Petroneis and Cosmioneis which together warranted their separation ( Round et al. 1990: 526); SEMs from a sample in the Davis collection from Saipan, CNMI ( Figs 96, 97 ), show the internal central raphe endings to be crozier- rather than anchor-shaped, suggesting that the Guam specimen is also Petroneis . However, C. delawariensis (Grunow ex Cleve) D.G. Mann ( Witkowski et al. 2000, pl. 106, figs 1, 2) is very similar in LM.

Figures

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.