Diatom assemblages in seasonally sea-ice-covered areas of the Sea of Okhotsk, a marginal sea of the western North Pacific, were investigated. We have selected diatom taxa relating to sea-ice coverage by comparing diatom assemblages in sea-ice, sinking-particle, and surface-sediment samples. The results of the study provide fundamental information for the reconstruction of past sea-ice cover based on ice-algal diatoms in sediments in the Sea of Okhotsk and the North Pacific.

To better understand radiolarian evolution and taxonomy, two middle Cambrian specimens recovered from Australia were studied using micro-CT. Analyses of their 3-D models revealed for the first time their skeletal architecture constructed of spicules. Insertion of an artificial sphere into their shells indicates that they may have secreted their spicules one by one during cell enlargement. The timing of skeletal genesis may be an important factor influencing the morphology of early radiolarians.