On ODP Leg 119, specimens collected of Eucampia antarctica (Castracane) Mangin var. antarctica exhibited morphological and distribution patterns that contrasted with those of Eucampia antarctica var. recta (Mangin) G. Fryxell et Prasad. E. antarctica var. antarctica was found over the northern Kerguelen Plateau, north of the summer Antarctic Convergence Zone, in the subpolar plankton and in the sediments. E. antarctica var. recta was found close to the continent in Prydz Bay. It was also collected near and under the ice in the northern Weddell Sea on a National Science Foundation Division of Polar Programs project (1983-1988).A key feature for distinguishing the two varieties in the field is the growth habit, with curvature in broad girdle view of the nominate, subpolar variety in both the winter stage and the more lightly silicified summer stage. A low ratio of terminal to intercalary valves results from the repeated division of the original doublets into chains of considerable length of the winter stage. Small spines around the elevations of one valve serve to clasp the sibling valve and maintain the chain formation. Cells of E. antarctica var. recta tend to be somewhat larger than E. antarctica var. antarctica, and they form chains that are straight in broad girdle view but slightly curved in narrow girdle view. There are no spines on an elevation of the valve, and a hyaline ring surrounds the pore field, forming a costate ocellus in the winter.This truly polar variety shows less growth in the winter stage, with a higher ratio of terminal to intercalary valves in Prydz Bay than that of the nominate variety from the subpolar regions over the Kerguelen Plateau.

Supplement to: Fryxell, Greta A (1991): Comparison of winter and summer growth stages of the diatom Eucampia antarctica from the Kerguelen Plateau and South of the Antarctic Convergence Zone. In: Barron, J; Larsen, B; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 119, 675-685