Rhoicosigma compactum (Greville) Grunow, 1877

Rhoicosigma compactum (Greville) Grunow Figs 139–143 View Figures 139–149

Ref. illus.: Van Heurck 1896, pl. 28, fig. 802; Peragallo & Peragallo 1897 –1908, pl. 35, fig. 8 Sample GU52N-7, GU52O-3; GU52P-1

Dimensions: Length 97–118 µm, width 16–23 µm, striae 20–22 in 10 µm.

Diagnostics: Frustule bent along the valvar plane (achnanthoid) ( Fig. 139 View Figures 139–149 ); raphe on concave/ventral valve highly sigmoid, the other (convex valve) nearly straight (as for the genus) ( Figs 140, 141, 143 View Figures 139–149 ). Plastids are several large plates ( Fig. 139 View Figures 139–149 ). Central raphe endings overlap on both valves ( Fig. 142 View Figures 139–149 ).

Comments: Hein & Lobban (2015) included two SEMs of this species for comparison with their new species R. parvum . Here I present full documentation of the record. Peragallo & Peragallo (1897 –1908) gave length = 77–180 µm, whereas Van Heurck (1896) gave rather larger dimensions of 140–180 x 35 µm, both gave stria density of 20–24 in 10 µm for R. compactum . R. oceanicum H. Peragallo ( Peragallo & Peragallo 1897 –1908, pl. 35, figs 3–7) is still larger (160–260 x 36– 45µm), with still coarser striae ( 17–18 in 10 µm). Hendey (1964, p. 250) gives dimensions of R. compactum as 90–150 µm, transapical striae 17–20 in 10 µm, longitudinal striae 22–24 in 10 µm, but he cites Peragallo & Peragallo (1897 –1908) figs 3, 4, 6, 7 and 8, whereas their figs 3–7 are identified as R. oceanicum .