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) Author Lobban, Christopher S. Division of Natural Sciences, University of Guam, Mangilao, GU 83823, USA e-mail: clobban @ guam. net clobban@guam.net text Micronesica 2015 2015 2 1 49 journal article 299054 10.5281/zenodo.12117576 9ec266f5-1dc7-4272-9fbc-67c7f2b0f5aa 0026-279X 12117576 Cocconeis subtilissima Meister Figs 27–32 Ref. illus.: De Stefano & Romero 2005 , pl. 32, figs 1–9, pl. 33, figs 1–11; Suzuki et al. 2008 , figs. 1–41; Riaux-Gobin et al. 2011 , pl. 6, figs 3–11, pl. 73, 74 Samples: GU44I-2, GU44Z-15, GU44AC-4, GU44AQ-1, GU52P-8 Dimensions: Length 16–22 µm, width 11–15 µm, striae (SV) 30 in 10 µm, ( RV ) 32 in 10 µm Diagnostics: RV ( Figs 29, 30 ) with sigmoid raphe branches, a small hyaline area beyond the terminal raphe endings; central area small, asymmetrical; internal central raphe endings deflect past each other and come to a point. SV alveolate ( Figs 31, 32 ) with slit-like striae divided by a single longitudinal hyaline line; internally a single row of areolae opens from the inner line of alveoli and the other alveolae open via a ring of areolae around the margin. Comments: De Stefano & Romero (2005) placed this species and others with such alveolate walls (e.g., C. convexa Giffen and C. heteroidea Meister in our flora) in a new section Alveolatae . They also provided tables comparing the alveolate taxa. De Stefano & Romero (2005) distinguish C. subtilissima from several species, especially C. pseudomarginata Gregory , by the denser striae. The RV of C. subtilissima is similar to that of C. krammeri (see especially Witkowski et al. 2000 , pl. 33, figs 1–4, pl. 42, fig. 34), but the stria density is slightly lower, 23–28 striae in 10 µm; on SV of C. krammeri there are 2 longitudinal hyaline lines creating three sets of areolae on each side of the sternum.