(Ehrenb.) Heiden, in Heiden & Kolbe (1928: 526, pl. 9, fig. 171)
Chaetoceros radiculum Castrac. (Castracane, 1886: 79, text fig.)?Chaetoceros schimperianus G.Karst. (Karsten, 1905: 117, pl. 15, fig. 2; pl. 16, fig. 4)?Chaetoceros bulbosus G.Karst. f. schimperiana (G.Karst.) Heiden, in Heiden & Kolbe (1928: 528, pl. 10, fig. 174; pl. 11, fig. 176), as schimperanaChaetoceros atlanticum f. bulbosum (Ehrenb.) Hargraves (1968: 26, figs 28–31)
Dicladia bulbosa Ehrenb. (Ehrenberg, 1844: 20; 1854, pl. 35A/21, fig. 10)
Hustedt (1958: 135), Moisan & Fryxell (1993: 493), Andreoli et al. (1995: fig. 8)
Cells solitary or in short chains, somewhat octagonal in girdle view; pervalvar axis 10–25 µm. Valves elliptical; apical axis 40–50 µm; surface flat, sloping towards the margins, with the centre slightly raised and with a conspicuous central process. Apertures large, although varying in size, somewhat rectangular. Setae strong, c. 20 µm long, arising from the valve surface slightly inside the margin, bulbous at their base, tapering distally (Fig. d); setae often striate, bearing lines of fine punctae. Chloroplasts small, spherical, numerous, distributed into the setae.
Coastal waters near Davis Station, East Antarctica; Weddell Sea (Buck & Garrison, 1983; Moison & Fryxell, 1993); Ross Sea (Watanabe, 1982; Andreoli et al., 1995); Weddell-Scotia Sea (Garrison et al., 1987); Lützow-Holm Bay (Tanimura et al., 1990); Prydz Bay, East Antarctica (Boden, 1985); Wilkes Land, Antarctica (Bunt & Wood, 1963); between the South Shetlands and Cabo de Hornos (Hendey, 1937, as C. radiculum); Southern Ocean, between 51° and 49°S, 0°08’ and 0°07’W, and 53°43’S 0°20’W, 49°S 0°07’W and 46°32’S 0°02’W (Hustedt, 1958); Southern Ocean–Davis Sea, 47–65°S (Heiden & Kolbe, 1928); KERFIX, 50°40’S 68°25’E, Southern Ocean (Kopczyńska et al., 1998).
Chaetoceros bulbosus was referred to by Priddle & Fryxell (1985) as “C. bulbosus complex”, including the atlanticus, bulbosus, schimperianus and cruciata phases. On morphological grounds, Hargraves (1968) suggested that C. bulbosus was a cold-water form of C. altlanticus, but he noted that the “type form also occurred at same stations as the form bulbosum”.