Seminavis robusta Danielidis & 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 : 15

Seminavis robusta Danielidis & D.G. Mann Figs 144, 145

Syn.: Seminavis ventricosa (Gregory) M. Garcia-Baptista ; Amphora ventricosa Gregory

Ref. illus.: Hendey 1964, pl. 38, fig. 12 (as Amphora ventricosa ); Navarro 1982b, fig. 16 (as Amphora angusta var. ventricosa ); Danielidis & Mann 2002, figs 39–53; Wachnicka & Gaiser 2007, figs 221–225; Hein et al. 2008, pl. 57, figs 3, 5; John 2012, figs 125 A–J, 126 A, B (as Seminavis ventricosa ); Stidolph et al. 2012, pl. 24, fig. 73 (as Amphora angusta var. ventricosa ) Samples: GU52Q-1a, GU52Q-10a

Dimensions: Length 65–74 µm, width 13–14 µm; dorsal striae strongly radiate at the center, 13–16 in 10 µm, less radiate toward the apices, 15–18 in 10 µm; ventral striae radiate at center, 14 in 10 µm, parallel toward apices, 16–18 in 10 µm.

Diagnostics: Semi-lanceolate valves, the raphe closer to the ventral side. Axial area asymmetrical, wider on the dorsal side (the hyaline areas seen in SEM to be grooves).

Comments: Differs from other (as yet unidentified) Seminavis spp. in our flora in the size and coarse striation. The most similar species is S. latior (A. Schmidt) Danielidis & D.G. Mann (2002, figs 35–41, and see Wachnicka & Gaiser 2007, figs 226, 227), in which the striae are uniformly spaced throughout, both 13–15 in 10 µm, and the ventral striae are radiate throughout, rather than parallel toward the apices. The width of our specimens matches the range given by Danielidis & Mann (2003) for S. latior and not S. robusta , but the range given by Wachnicka & Gaiser (2007) encompasses our broader specimens. More clearly distinct are S. basilica Danielidis ( Danielidis & Mann 2003, figs 1–19), which has denser (19–25 in 10 µm), parallel striae throughout on both ventral and dorsal surfaces, and S. insignis Álvarez-Blanco & S. Blanco (2014) , 20–26 dorsal striae in 10 µm.