2020 Volume 36 Pages 35-45
A new diatom species, Eupyxidicula atlantica sp. nov., is described from upper Pliocene–lower Pleistocene sediments in the subpolar North Atlantic. Vegetative valves of the new species are domed and have a tubular process with an internal rimoportula, large loculate areolae arranged in a quincunx pattern over the valve, and mantle rimoportulae each with an external simple opening. Resting spore valves have additional rimoportulae scattered over the valve. The tubular process is the most important feature for distinguishing species of the genus Eupyxidicula. In E. atlantica, one (sometimes two) tubular process is found vertically in the valve center and has a hook structure in the middle and a notch at the apex. These characteristic features of the tubular process suggest that the linkage of cell colonies of E. atlantica was weaker than that of other Eupyxidicula species, e.g., E. turris and E. nipponicus, which have many tubular processes on the valve face/mantle area junction. Eupyxidicula atlantica can be differentiated from extant E. turris, E. nipponicus, and E. palmeriana not only by this unique tubular process but also by internal areolar cribra. The cribra of E. atlantica are restricted within hexagonal floors of areolae, whereas those of extant species are continuously distributed from the valve center to the margin. Among fossil species, Stephanopyxis apiculata is similar to E. atlantica in that both species have tubular processes at the valve center. In contrast to E. atlantica, however, S. apiculata has 0–4 tubular processes with no hook and notch structure, and their length depends upon the degree of curvature of valves.
