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.