Hemidiscus cuneiformis var. ventricosa (Castracane) Hustedt, 1930

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 : 5

Hemidiscus cuneiformis var. ventricosa (Castracane) Hustedt Figs 41, 42

COSCINODISCALES Round & Crawford : Hemidiscaceae Hendey

Ref. illus.: Hustedt 1927 –1930, fig. 542d; Hendey 1964, pl. 22, fig. 9; Ricard 1987, figs 30–34; Stidolph et al. 2012, pl. 13, fig. 71 and pl. 4, figs 104, 107; Álvarez-Blanco & Blanco 2014, pl. 11, fig. 6; the images in Round et al. 1990, pp. 192–193, are also evidently this species.

Samples: GU66F-4

Dimensions: long axis 71–74 µm, short axis 41–45 µm

Diagnostics: Distinctively shaped, lens-shaped in valve view but the frustules wedge-shaped (cuneiform) because the valve faces are at an angle to one another. Areola pattern similar to Actinocyclus , to which it is related, but with a series of radiating patterns around the margin, especially on the less strongly curved side. Large rimoportulae visible in the oblique view ( Fig. 42 ). A pseudonodulus is present on the flatter side ( Fig. 41 ).

Comments: Two valves observed in one sample. The ventral curvatures of H. cuneiformis Wallich vary from straight to sinuous and Hustedt combined several older Eudotia species as varieties. Images shown by Hendey (1964), Stidolph et al. (2012, pl. 13, fig. 71) and identified simply as H. cuneiformis Wallich , have a ventral outline as shown here; Hendey did not comment on varieties; Stidolph et al. (2012, pl. 10, fig. 30) show the nominate variety, again without noting the variety. The species differs further in valve shape from two fossil species ( Harwood & Maruyama 1992). Although Round et al. (1990) (reprinted in AlgaeBase) said that the valves are cuneiform, it seems to me that Wallich’s (1860) epithet refers to the shape of the frustule (described by Round et al. 1990 as “shaped like orange segments”), rather than to the shape of the valve.

Figures

Figures 41–50. Figs 41, 42. Hemidiscus cuneiformis var. ventricosa (GU66F-4) (DIC). Fig. 41. Valve view; arrow points to pseudonodulus. Fig. 42. Oblique view with focus on several of the rimoportulae (arrow). Figs 43–48. Lauderia excentrica. Fig. 43. Holotype specimen (GU44I-1) (DIC). Fig. 44. External view of valve showing excentric, reniform annulus and external rimoportula opening (arrow) (GU44Y-13) (SEM). Fig. 45. External detail of annulus (GU55B-4) (SEM). Fig. 46. Internal view of valve with rimoportula (arrow), also showing the external aspect of the fultoportulae along the bottom rim (GY44Y-13) (SEM). Figs 47, 48. External and internal details of striae and fultoportulae, showing 5 satellite pores in the central fultoportulae (arrowhead) and 2-4 in the striae (arrow) (GU44Y-13) (SEM). Figs 49, 50. Mastogloia affirmata valve and valvocopula at two focal planes (GU44AX-1) (DIC). Scale bars: Figs 41, 42, 49, 50 = 10 µm, Figs 43, 44, 46 = 5 µm, Figs 45, 47, 48 = 2 µm.