Cocconeis subtilissima Meister, 1934

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 : 4

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.

Figures

Figures 22–40. Figs 22–26. Cocconeis ornata, two valves at two focal planes each in DIC and external view in SEM (GU44AU-2). Figs 27–32. Cocconeis subtilissima. Figs 27, 28. Frustules in LM (GU44I-2, GU44Z-15) (DIC). Figs 29, 30. RV external and internal with valvocopula (GU44AQ-1). Figs 31, 32. SV external (whole mount, GU44AC-4), showing the alveolae at the fracture (arrow), and internal (GU44AQ-1). Figs 33–40. Colliculoamphora gabgabensis. Fig. 33. Holotype specimen (GU44AK-6) (DIC). Fig. 34. Paratype specimen (GU44I-1) (DIC). Fig. 35. Specimen showing deeper indentation (GU44AK-6). Figs 36–38. External views, showing the eunotid position of the raphe; arrows on Fig. 37 indicate short striae; Fig. 38 shows girdle bands (GU44AK-6, GU44Z-15, GU52Q-10a, respectively) (SEM). Figs 39, 40. Internal views (GU44W- 10, GU44K-6) (SEM). Scale bars: Figs 22–36 = 5 µm, Figs 37, 38 = 2.5 µm, Figs 39, 40 = 2 µm.