Cleve Manguin (1960: 274, pl. 8, fig. 89)
?Chaetoceros pendulus G.Karst. (Karsten, 1905: 118, pl. 15, fig. 7) (see Hasle & Syvertsen, 1997)
Priddle & Fryxell (1985: 22, fig. on p. 23), Hasle & Syvertsen (1997: 193, pl. 38, tab. 46)
Cells solitary, heterovalvate, rectangular in girdle view; pervalvar axis 6.5–9 µm. Valves elliptical; apical axis 10–11 µm, with a small off-centre tubular extension of the process. Setae long, coarse, spinose; setae on the upper valve slightly enlarged at the point of emergence from inside the valve margin, curving downwards and becoming convergent towards their ends; setae from lower valve ±parallel to pervalvar axis.
Coastal waters near Davis Station, East Antarctica; type locality, Terre Adélie, 63°25’S 143°09’E (Manguin, 1960).
The type variety is regarded as a warm-water diatom, Hendey (1937) recording it as “an oceanic species, widely spread throughout the Indian Ocean”. The only morphological differences between the var. aequatorialis and var. antarcticus seem to be the size (apical axes c. 25 µm and 10–11 µm, respectively) and the orientation of the setae that arise from the upper valve; those of the type variety remain parallel for their entire length, while those of var. antarcticus converge distally. Chaetoceros pendulus has a similar morphology to C. aequatorialis var. antarcticus, but it has smooth rather than spinose setae.